# sqlite/sqlite — codebase unpack

> Canonical page: https://codevetter.com/unpack/sqlite

This is a deterministic Repo Unpack scan of sqlite/sqlite — a structural map, not a review, security audit, or maintainer-endorsed description.

- Scanned commit: fde3a84dddf35f4c19797c8afad04a44c596f4d8 (2026-09-21)
- Last upstream commit: Latest preprocessor for various cleanups and fixes. Duplicate the tester1 concurrency warning in the worker-based copy.
- Generated by codevetter 1.12.0 on 2026-09-22
- 2207 files scanned · 34.5 MB

## Languages

- C: 357 files
- Java: 58 files
- JavaScript: 42 files
- Markdown: 27 files
- HTML: 21 files
- SQL: 14 files
- Shell: 14 files
- C#: 2 files

## Repository structure

- test/ — 1285 files
- ext/ — 593 files
- src/ — 154 files
- tool/ — 95 files
- autosetup/ — 22 files
- autoconf/ — 15 files
- doc/ — 13 files
- mptest/ — 6 files

Probable source entrypoint: `src/` (inferred from the tree, not upstream docs)

## Structural health signals

Average score 7.7/10 across 93 files; 24 hotspots. These are deterministic review leads, not proof of a bug.

## Recent history

- fde3a84dddf3 (2026-09-21) Latest preprocessor for various cleanups and fixes. Duplicate the tester1 concurrency warning in the worker-based copy.
- 5636f0f4a4c9 (2026-09-21) Fix potential buffer overreads in demo program ext/fts3/tool/fts3view.c. Bug [bugs:/info/2026-09-21T13:50:52Z | 2026-09-21T13:50:52Z].
- 9fe7e4dd3127 (2026-09-21) Update sessionChangesetFindTable() so that it honors the contract defined in its header comment and always returns non-zero if the table is not found.
- 3a81fb982969 (2026-09-21) Teach 'make libtcl' to honor the --disable-rpath configure flag. Addresses [forum:2026-09-21T10:24:56Z|forum post 2026-09-21T10:24:56Z].
- 5f8b6a782de3 (2026-09-21) Fix truncation of 64-bit integer values passed to the fts3 snippet() function. Report [bugs:/info/2026-09-21T02:41:49Z | 2026-09-21T02:41:49Z].

## Overview

This is the canonical source tree for SQLite 3.54.0 (VERSION, manifest.uuid `c9b4695f...`) — a serverless, zero-configuration, public-domain SQL database engine implemented as a C library that compiles down to a single-file amalgamation (`sqlite3.c`). The tree is far more than the library: it also carries the `sqlite3` CLI shell (`src/shell.c.in`, ~14.9k lines with ~40 dot-commands), a dozen major extensions under `ext/` (FTS3/5, R-Tree/Geopoly, session/changesets, RBU, recover, intck, JNI bindings, a WASM/OPFS browser build), a TCL binding, and an unusually large test apparatus (1,195 `.test` scripts plus fuzzers). It is distinctive for being managed in Fossil rather than Git (this GitHub remote is a mirror), for refusing pull requests and agentic code on copyright grounds (AGENTS.md), for generating much of its own C (parser, opcodes, pragma table, keyword hash) from TCL/Lemon tooling, and for a testing culture where `make devtest` is the minimum bar before any check-in.

## System map

The library is a layered stack inside one process: SQL text enters the tokenizer, goes through a Lemon-generated LALR(1) parser into a code generator, is optimized by the `where*.c` planner, and is executed as bytecode by the VDBE, which reaches storage through B-Tree → Pager → WAL → VFS. There is no daemon and no network boundary in the core; the only OS boundary is the `sqlite3_vfs` interface, implemented by `os_unix.c`, `os_win.c`, `os_kv.c` (key/value / browser localStorage) and `memdb.c`. Build is driven by autosetup (JimTCL-compatible), not GNU Autoconf, with `main.mk` holding the real rules and `Makefile.msc` mirroring them for MSVC. Deployment shape is a static/shared library plus the amalgamation tarball, the `sqlite3` CLI, and auxiliary binaries (`sqldiff`, `sqlite3_rsync`, `sqlite3_analyzer`, `testfixture`, `fuzzcheck`). Version control is Fossil; `manifest`, `manifest.uuid`, and `.fossil-settings/` are Fossil artifacts carried into the Git mirror.
- The public C API is defined by the template `src/sqlite.h.in` (11,463 lines), which `tool/mksqlite3h.tcl` expands into the deliverable `sqlite3.h` by splicing in `VERSION` (3.54.0) and the SHA3 check-in id from `manifest.uuid`. — [src/sqlite.h.in](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/sqlite.h.in) [tool/mksqlite3h.tcl](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/mksqlite3h.tcl) [VERSION](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/VERSION) [manifest.uuid](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/manifest.uuid) [README.md#L230-L246](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/README.md#L230-L246)
- `openDatabase()` in `src/main.c:3388` is the single funnel for `sqlite3_open`, `sqlite3_open_v2` and `sqlite3_open16`: it calls `sqlite3_initialize()`, decides thread-safety from `SQLITE_OPEN_NOMUTEX`/`FULLMUTEX` vs `sqlite3GlobalConfig.bFullMutex`, masks off internal-only open flags, allocates the `sqlite3` handle with `sqlite3MallocZero`, and enables lookaside plus `sqlite3_wal_autocheckpoint`. — [src/main.c#L3388-L3470](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/main.c#L3388-L3470) [src/main.c#L3753-L3772](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/main.c#L3753-L3772)
- Compilation runs through `sqlite3LockAndPrepare()` (`src/prepare.c:854`), which takes `db->mutex`, calls `sqlite3BtreeEnterAll()` to hold every B-Tree mutex, and retries `sqlite3Prepare()` on `SQLITE_ERROR_RETRY` / `SQLITE_SCHEMA` up to `SQLITE_MAX_PREPARE_RETRY`. — [src/prepare.c#L854-L900](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/prepare.c#L854-L900)
- The VDBE is the execution boundary: `sqlite3VdbeExec()` (`src/vdbe.c:902`) is one giant `for(pOp=&aOp[p->pc]; 1; pOp++)` dispatch loop over 190 `case OP_*` handlers, and `tool/mkopcodeh.tcl` scrapes those `case OP_` lines out of `vdbe.c` to assign opcode numbers. — [src/vdbe.c#L902-L990](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/vdbe.c#L902-L990) [tool/mkopcodeh.tcl](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/mkopcodeh.tcl) [AGENTS.md](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/AGENTS.md)
- Storage is layered strictly: `src/btree.c` (407KB, the largest file) exposes `sqlite3BtreeOpen/BeginTrans/Cursor/CommitPhaseOne/CommitPhaseTwo`, which sits on `src/pager.c`'s `sqlite3PagerOpen/Get/Write/CommitPhaseOne`, which in turn either journals or writes WAL frames via `src/wal.c`'s `sqlite3WalFrames`/`sqlite3WalCheckpoint`. — [src/btree.c#L2562-L2570](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/btree.c#L2562-L2570) [src/pager.c#L4789](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/pager.c#L4789) [src/pager.c#L6527-L6580](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/pager.c#L6527-L6580) [src/wal.c#L4361-L4390](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/wal.c#L4361-L4390)
- The OS boundary is a registry of `sqlite3_vfs` objects; `os_unix.c` registers up to 12 named VFSes (`unix`, `unix-none`, `unix-dotfile`, `unix-excl`, `unix-flock`, `unix-afp`, `unix-nfs`, `unix-proxy`, …) via a `UNIXVFS()` macro table at `src/os_unix.c:8497`, each pairing a locking style with an `IOMETHODS()`-generated `sqlite3_io_methods` vtable. — [src/os_unix.c#L5808-L5945](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/os_unix.c#L5808-L5945) [src/os_unix.c#L8465-L8536](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/os_unix.c#L8465-L8536)
- Alternative VFS backends ship in-tree: `src/memdb.c` registers a `memdb` VFS backing `sqlite3_serialize`/`sqlite3_deserialize`, and `src/os_kv.c` registers `kvvfs`, the key/value VFS used by the WASM/browser build. — [src/memdb.c#L750-L935](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/memdb.c#L750-L935) [src/os_kv.c#L1086-L1095](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/os_kv.c#L1086-L1095)
- The build entrypoint is `./configure`, a 4-line shell wrapper that execs autosetup; `auto.def` drives it via `sqlite-configure canonical`, where `--dev` implies `--all --debug`, disables the amalgamation, and sets `CFLAGS=-O0 -g`. — [configure](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/configure) [auto.def#L20-L35](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/auto.def#L20-L35) [autosetup/sqlite-config.tcl#L160-L250](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/autosetup/sqlite-config.tcl#L160-L250)
- `main.mk` is the real makefile body (84KB): it defines `LIBOBJS0` (per-file objects) vs `LIBOBJS1 = sqlite3.o` (amalgamation) selected by `USE_AMALGAMATION`, and builds `sqlite3.c` by running `tool/mksqlite3c.tcl` over a generated `tsrc/` directory. — [main.mk#L529-L565](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/main.mk#L529-L565) [main.mk#L1145-L1152](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/main.mk#L1145-L1152) [tool/mksqlite3c.tcl#L1-L25](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/mksqlite3c.tcl#L1-L25)
- The CLI shell is generated, not compiled directly: `src/shell.c.in` uses `INCLUDE ../ext/...` directives (processed by `tool/mkshellc.tcl`) to inline ~25 extension source files — sha1/shathree, base64/base85, decimal, ieee754, series, regexp, fileio, completion, appendvfs, zipfile, sqlar, vfstrace, diskused, plus the `expert`, `intck`, `recover` and `qrf` libraries. — [src/shell.c.in#L259-L326](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L259-L326) [tool/mkshellc.tcl](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/mkshellc.tcl)
- Auxiliary deliverables live in `tool/`: `sqldiff.c` (database diffing), `sqlite3_rsync.c` (rsync-like replication over SSH), `sqlite3_analyzer.c.in` (space analysis, paired with `tool/spaceanal.tcl`), `showdb.c`/`showwal.c`/`showjournal.c` (file-format forensics), and `lemon.c` (the parser generator itself). — [tool/sqldiff.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/sqldiff.c) [tool/sqlite3_rsync.c#L23-L40](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/sqlite3_rsync.c#L23-L40) [tool/spaceanal.tcl](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/spaceanal.tcl) [tool/showwal.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/showwal.c) [tool/lemon.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/lemon.c)
- A second, reduced build tree exists under `autoconf/` for the shipped amalgamation tarball (its own `auto.def`, `Makefile.in`, `Makefile.msc`, `Makefile.fallback`, plus a `tea/` TCL Extension Architecture build), and `tool/srctree-check.tcl` enforces that `autoconf/Makefile.msc` stays in sync with the top-level `Makefile.msc`. — [autoconf/README.first](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/autoconf/README.first) [autoconf/Makefile.msc](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/autoconf/Makefile.msc) [tool/srctree-check.tcl#L37-L45](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/srctree-check.tcl#L37-L45)
- There is no CI configuration in the repository — no `.github/`, `.gitlab-ci.yml`, or Travis file exists; the only VCS metadata is `.fossil-settings/` (`binary-glob`, `empty-dirs`, `ignore-glob`) plus the Fossil `manifest`, consistent with the README's statement that the Git remote is a mirror. — [.fossil-settings/ignore-glob](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/.fossil-settings/ignore-glob) [manifest.uuid](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/manifest.uuid) [README.md#L13-L30](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/README.md#L13-L30)
- Language-binding boundaries ship in-tree: `src/tclsqlite.c` (150KB) exposes `Sqlite3_Init`/`DbMain`/`DbObjCmd` as a TCL package, `ext/jni/src/c/sqlite3-jni.c` with 58 Java files provides JNI bindings, and `ext/wasm/api/` provides an Emscripten/WASM JS API with OPFS-backed VFS variants. — [src/tclsqlite.c#L4310-L4513](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/tclsqlite.c#L4310-L4513) [ext/jni/src/c/sqlite3-jni.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/jni/src/c/sqlite3-jni.c) [ext/wasm/api/sqlite3-api-oo1.c-pp.js](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/wasm/api/sqlite3-api-oo1.c-pp.js) [ext/wasm/api/sqlite3-vfs-opfs.c-pp.js](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/wasm/api/sqlite3-vfs-opfs.c-pp.js)

## Feature catalog

User-facing surface splits three ways: the C API in `sqlite.h.in`, the `sqlite3` CLI's dot-command language, and the loadable/compiled-in extension set. The CLI carries roughly 40 dot-commands covering schema inspection, import/export, archives, diagnostics, and integrity checking, plus 23 result-output modes now rendered by the new `ext/qrf` formatting library. Extensions add full-text search, spatial indexing, changeset/session replication, incremental update (RBU), corruption recovery, index recommendation, and a large `ext/misc/` grab-bag of 60 single-file functions and virtual tables. Configure-time feature flags (`--all` implies fts4, fts5, rtree, geopoly, session, dbpage, dbstat, carray) decide what lands in the amalgamation.
- `do_meta_command()` (`src/shell.c.in:9947`) dispatches ~40 dot-commands including `.archive`, `.auth`, `.clone`, `.dump`, `.eqp`, `.expert`, `.explain`, `.filectrl`, `.fullschema`, `.import`, `.imposter`, `.intck`, `.iotrace`, `.load`, `.log`, `.mode`, `.open`, `.recover`, `.schema`, `.session`, `.stats`, `.vfsinfo`, `.vfslist`, `.vfsname` and `.wheretrace`. — [src/shell.c.in#L9947-L10060](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L9947-L10060)
- The shell supports 23 output modes enumerated in the `aModeInfo[]` table at `src/shell.c.in:618` — ascii, box, c, column, count, csv, html, insert, jatom, jobject, json, line, list, markdown, off, psql, qbox, quote, split, table, tabs, tcl, www — each mapping to a QRF style plus separator/quoting/alignment settings. — [src/shell.c.in#L618-L658](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L618-L658)
- Result formatting was factored out into a new library `ext/qrf/` (headed `2025-10-20`) whose `sqlite3_qrf_spec` struct carries style, escaping, quoting, word-wrap, column widths, alignment, screen width and `xRender`/`xWrite` callbacks; `shell_exec()` copies `pArg->mode.spec` into a local spec and installs `shellWriteQR` as the writer. — [ext/qrf/qrf.h#L1-L60](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/qrf/qrf.h#L1-L60) [src/shell.c.in#L3807-L3845](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L3807-L3845)
- `open_db()` auto-registers a fixed extension set on every connection: sha/shathree, uint, stmtrand, decimal, base64, base85, regexp, ieee754, series, diskused, strdup, and (outside the WASM fiddle build) fileio and completion; zipfile and sqlar are added when `SQLITE_HAVE_ZLIB` is defined and safe mode is off. — [src/shell.c.in#L5155-L5182](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L5155-L5182)
- The shell can open databases in four modes chosen by `deduceDatabaseType()` — normal file, append-VFS (`apndvfs`), ZIP archive (opened as `:memory:`), and hex-dump/deserialize — with `~/` expanded against `$HOME` when the literal path does not exist. — [src/shell.c.in#L5069-L5130](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L5069-L5130)
- FTS5 is a full subsystem of 15 C files (`fts5_index.c`, `fts5_expr.c`, `fts5_storage.c`, `fts5_tokenize.c`, `fts5_vocab.c`, …) exposing a public `fts5_api` struct with `xCreateTokenizer`, `xCreateTokenizer_v2` and `xCreateFunction` for third-party tokenizers and auxiliary ranking functions. — [ext/fts5/fts5.h#L350-L360](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/fts5/fts5.h#L350-L360) [ext/fts5/fts5.h#L696-L735](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/fts5/fts5.h#L696-L735) [ext/fts5/fts5_index.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/fts5/fts5_index.c)
- The session extension implements changeset capture and replay: `sqlite3session_create`, `sqlite3session_attach`, `sqlite3session_changeset` (plus `_strm` streaming variants) and three generations of apply APIs — `sqlite3changeset_apply`, `_apply_v2`, `_apply_v3` — each with streaming counterparts. — [ext/session/sqlite3session.c#L2362-L2480](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/session/sqlite3session.c#L2362-L2480) [ext/session/sqlite3session.c#L3213-L3240](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/session/sqlite3session.c#L3213-L3240) [ext/session/sqlite3session.c#L5882-L6020](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/session/sqlite3session.c#L5882-L6020)
- Database recovery is a first-class feature: `ext/recover/sqlite3recover.c` plus `dbdata.c` implement the `.recover` dot-command by walking raw pages of a corrupt file, and are compiled into the CLI via `INCLUDE` directives. — [ext/recover/sqlite3recover.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/recover/sqlite3recover.c) [ext/recover/dbdata.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/recover/dbdata.c) [src/shell.c.in#L323-L326](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L323-L326)
- The `.expert` command exposes `ext/expert/sqlite3expert.c`, which analyzes a query workload and recommends indexes; `shell_exec()` short-circuits to `expertHandleSQL()` whenever `pArg->expert.pExpert` is active. — [ext/expert/sqlite3expert.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/expert/sqlite3expert.c) [src/shell.c.in#L3845-L3850](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L3845-L3850) [src/shell.c.in#L307-L308](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L307-L308)
- `.intck` runs the incremental integrity-check library `ext/intck/sqlite3intck.c`, an alternative to `PRAGMA integrity_check` that can be run in bounded steps; it ships with its own six-file test suite. — [ext/intck/sqlite3intck.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/intck/sqlite3intck.c) [ext/intck/intck1.test](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/intck/intck1.test) [src/shell.c.in#L310-L311](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L310-L311)
- `ext/misc/` holds 60 single-file extensions (series, regexp, fileio, decimal, base64/base85, uint, sha1/shathree, appendvfs, vfstrace, zipfile, sqlar, completion, memtrace, pcachetrace, diskused, …), most of which are excluded from the core amalgamation but compiled into the CLI. — [ext/misc/fileio.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/misc/fileio.c) [ext/misc/series.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/misc/series.c) [ext/misc/vfstrace.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/misc/vfstrace.c) [src/shell.c.in#L285-L315](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L285-L315)
- In-memory serialization is a supported API path: `sqlite3_serialize()` (`src/memdb.c:750`) and `sqlite3_deserialize()` (`src/memdb.c:841`) move whole database images in and out of process memory, which is also what the shell's hex-db/deserialize open mode relies on. — [src/memdb.c#L750-L860](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/memdb.c#L750-L860) [src/shell.c.in#L5113-L5118](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L5113-L5118)
- Online backup is exposed through `sqlite3_backup_init`/`_step`/`_finish` in `src/backup.c`, and the pager cooperates by calling `sqlite3BackupRestart()` when a commit would invalidate an in-progress backup. — [src/backup.c#L141](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/backup.c#L141) [src/backup.c#L325](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/backup.c#L325) [src/backup.c#L598](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/backup.c#L598) [src/pager.c#L6554-L6558](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/pager.c#L6554-L6558)
- Feature selection is exposed as configure flags declared in `autosetup/sqlite-config.tcl`: `--threadsafe`, `--load-extension`, `--math`, `--json`, `--memsys3/5`, `--fts3/4/5`, `--rtree`, `--geopoly`, `--session`, `--dbpage`, `--dbstat`, `--carray`, `--update-limit`, `--column-metadata`, with `--all` expanding to `{fts4 fts5 rtree geopoly session dbpage dbstat carray}`. — [autosetup/sqlite-config.tcl#L60-L72](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/autosetup/sqlite-config.tcl#L60-L72) [autosetup/sqlite-config.tcl#L205-L240](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/autosetup/sqlite-config.tcl#L205-L240)
- `sqlite3_rsync` is a network-facing feature: it syncs a live database between a local path and a `USER@HOST:PATH` remote, with `--ssh`, `--port`, `--exe`, `--protocol` and `--wal-only` options. — [tool/sqlite3_rsync.c#L23-L40](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/sqlite3_rsync.c#L23-L40) [tool/sqlite3_rsync.c#L2058-L2120](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/sqlite3_rsync.c#L2058-L2120)

## Data flow

Data enters as UTF-8 (or UTF-16, transcoded at the API edge) SQL text or as bound parameter values. `sqlite3RunParser` drives `sqlite3GetToken` token-by-token into the Lemon parser, which builds `Select`/`Expr`/`SrcList` trees inside a `Parse` object; the code generators turn those trees into a VDBE program of `Op` records. At run time the VDBE owns register memory (`Mem *aMem`) and cursors; reads and writes go through B-Tree cursors into the pager's page cache, and out to disk either as rollback-journal writes or WAL frame appends, always via `sqlite3_vfs` methods. Output leaves either as `sqlite3_column_*` values pulled from `p->pResultRow`, or — in the CLI — through QRF's `xWrite` callback into a `FILE*`. Schema itself round-trips through this same machinery: `sqlite3_schema` rows are re-parsed on load, which is why a schema cookie mismatch forces `sqlite3Reprepare`.
- Text input is bounded at the tokenizer: `sqlite3RunParser` decrements `mxSqlLen` (initialized from `db->aLimit[SQLITE_LIMIT_SQL_LENGTH]`) by each token length and aborts with `SQLITE_TOOBIG` when it goes negative. — [src/tokenize.c#L600-L655](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/tokenize.c#L600-L655)
- The tokenizer→parser handoff is a push loop: `sqlite3GetToken()` returns a token type and length, context-sensitive keywords are disambiguated by `analyzeWindowKeyword`/`analyzeOverKeyword`/`analyzeFilterKeyword`, and each token is pushed into the Lemon engine with `sqlite3Parser(pEngine, tokenType, pParse->sLastToken)`. — [src/tokenize.c#L644-L715](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/tokenize.c#L644-L715)
- At end of input the parser is deliberately fed two synthetic tokens — `TK_SEMI` then `0` — so the grammar can reduce cleanly without a trailing semicolon in the source text. — [src/tokenize.c#L672-L684](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/tokenize.c#L672-L684)
- SQL comments are conditionally dropped in the token stream rather than the grammar: `TK_COMMENT` is skipped only when `db->init.busy` (schema reparse) or `SQLITE_DBCONFIG_ENABLE_COMMENTS` is on, otherwise it falls through to an 'unrecognized token' error. — [src/tokenize.c#L697-L706](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/tokenize.c#L697-L706)
- UTF-16 inputs are normalized at the boundary: `sqlite3_open16` converts the filename via `sqlite3ValueText(pVal, SQLITE_UTF8)` before calling `openDatabase`, and sets `SCHEMA_ENC`/`ENC` to `SQLITE_UTF16NATIVE` if the schema has not yet loaded. — [src/main.c#L3773-L3805](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/main.c#L3773-L3805)
- Query plans are produced by `sqlite3WhereBegin()`, which chooses the nesting order of FROM-clause tables based on available indexes rather than written order, and emits the cursor-opening code that `sqlite3WhereEnd()` later closes. — [src/where.c#L6770-L6845](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/where.c#L6770-L6845) [src/where.c#L7541](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/where.c#L7541)
- `sqlite3Select()` is the funnel for all query code generation; it takes a `SelectDest` describing where rows go (`SRT_Output`, `SRT_Exists`, `SRT_Fifo`, `SRT_DistQueue`, …), so the same tree compiler serves top-level queries, subqueries, and recursive CTE queues. — [src/select.c#L7680-L7735](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/select.c#L7680-L7735)
- Dirty-page flow at commit is branch-per-journal-mode inside `sqlite3PagerCommitPhaseOne`: in WAL mode it takes `sqlite3PcacheDirtyList()` and calls `pagerWalFrames()` (forcing page 1 into the list if empty, per ticket 2d1a5c67dfc2363e), otherwise it goes down the rollback-journal or batch-atomic-write path. — [src/pager.c#L6551-L6600](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/pager.c#L6551-L6600) [src/pager.c#L3233](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/pager.c#L3233)
- The pager state machine is explicit: `sqlite3PagerCommitPhaseOne` asserts the pager is in `PAGER_WRITER_LOCKED`, `WRITER_CACHEMOD`, `WRITER_DBMOD` or `PAGER_ERROR`, and returns early if it has not reached `PAGER_WRITER_CACHEMOD` (i.e. nothing was modified). — [src/pager.c#L6533-L6552](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/pager.c#L6533-L6552) [doc/pager-invariants.txt](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/doc/pager-invariants.txt)
- WAL readers snapshot through `sqlite3WalBeginReadTransaction` → `walTryBeginRead` → `walIndexReadHdr`, which reads the shared-memory wal-index header; the shm region itself is created by `unixOpenSharedMemory`/`unixLockSharedMemory` in the unix VFS. — [src/wal.c#L3575](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/wal.c#L3575) [src/wal.c#L3102](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/wal.c#L3102) [src/wal.c#L2742](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/wal.c#L2742) [src/os_unix.c#L4850-L5040](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/os_unix.c#L4850-L5040) [doc/wal-lock.md](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/doc/wal-lock.md)
- In the CLI the output boundary is `shell_exec()`: it loops `sqlite3_prepare_v2` over the input buffer using `zLeftover` to advance through multi-statement text, and renders each result set through the QRF spec whose `xWrite` is `shellWriteQR`. — [src/shell.c.in#L3807-L3875](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L3807-L3875)
- Interactive input is accumulated line-by-line in `process_input()`, which grows `zSql` by half-again increments, treats a leading `.` or `#` on a fresh buffer as a dot-command, and only executes when a semicolon is present *and* `sqlite3_complete(zSql)` agrees the statement is finished. — [src/shell.c.in#L13473-L13560](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L13473-L13560)
- Result rows are owned by the VDBE and invalidated on the next step: `sqlite3Step` returns `SQLITE_ROW` with `p->pResultRow` set, and clears `p->pResultRow = 0` on any non-ROW outcome before running WAL callbacks or transferring errors. — [src/vdbeapi.c#L930-L960](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/vdbeapi.c#L930-L960)
- Error state flows through two channels that must be kept consistent — the per-statement `p->rc` and the per-connection `db->errCode` — reconciled by `sqlite3VdbeTransferError()` only for statements prepared with `SQLITE_PREPARE_SAVESQL`. — [src/vdbeapi.c#L946-L970](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/vdbeapi.c#L946-L970) [src/prepare.c#L955-L972](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/prepare.c#L955-L972)

## Behavior traces

Three flows carry most of the system's weight: library startup and connection open; the prepare/step/finalize query cycle including automatic recompilation on schema change; and the CLI's REPL loop from argv parsing through dot-command dispatch to statement execution. A fourth, the durability path, is worth tracing separately because commit behavior forks sharply between rollback-journal and WAL mode. Each trace below names the actual functions in call order as read from the sources.
- Connection open trace: `sqlite3_open_v2` → `openDatabase` → `sqlite3_initialize` → mutex decision → flag masking → `sqlite3MallocZero(sizeof(sqlite3))` → `sqlite3MutexAlloc(SQLITE_MUTEX_RECURSIVE)` → `sqlite3_mutex_enter` → `db->eOpenState = SQLITE_STATE_BUSY` → … → `setupLookaside` → `sqlite3_wal_autocheckpoint` → `opendb_out` label, which closes and nulls the handle on OOM or marks it `SQLITE_STATE_SICK` on other errors. — [src/main.c#L3388-L3470](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/main.c#L3388-L3470) [src/main.c#L3700-L3752](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/main.c#L3700-L3752)
- Prepare trace: `sqlite3_prepare_v2` → `sqlite3LockAndPrepare(db, zSql, nBytes, SQLITE_PREPARE_SAVESQL, 0, …)` → `sqlite3_mutex_enter(db->mutex)` → `sqlite3BtreeEnterAll(db)` → `sqlite3Prepare` (which memsets the `Parse` header/tail, links `sParse.pOuterParse`, and runs the parser) → retry loop → `sqlite3BtreeLeaveAll` → `sqlite3ApiExit` → `db->busyHandler.nBusy = 0`. — [src/prepare.c#L700-L745](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/prepare.c#L700-L745) [src/prepare.c#L854-L900](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/prepare.c#L854-L900) [src/prepare.c#L955-L972](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/prepare.c#L955-L972)
- `SQLITE_PREPARE_PERSISTENT` changes allocation strategy mid-prepare: `sqlite3Prepare` increments `sParse.disableLookaside` and invokes `DisableLookaside` so long-lived statements do not pin lookaside slabs. — [src/prepare.c#L734-L740](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/prepare.c#L734-L740)
- Step trace: `sqlite3_step` → `vdbeSafetyNotNull` → `sqlite3_mutex_enter` → inner `sqlite3Step` → (READY state) reset interrupt flag, bump `db->nVdbeActive`/`nVdbeWrite`/`nVdbeRead`, set `p->pc = 0`, move to `VDBE_RUN_STATE` → `sqlite3VdbeExec` (or `sqlite3VdbeList` when explaining) → on `SQLITE_DONE` with autocommit, `doWalCallbacks(db)`. — [src/vdbeapi.c#L838-L950](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/vdbeapi.c#L838-L950) [src/vdbeapi.c#L980-L1000](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/vdbeapi.c#L980-L1000)
- Auto-reset trace: when `sqlite3_step` is called on a statement already in `VDBE_HALT_STATE`, `sqlite3Step` calls `sqlite3_reset()` and `goto restart_step` — behavior introduced in 3.7.0, with `SQLITE_OMIT_AUTORESET` restoring the pre-3.6.23 `SQLITE_MISUSE` return. — [src/vdbeapi.c#L887-L917](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/vdbeapi.c#L887-L917)
- Schema-change recovery trace: `sqlite3_step` loops while `sqlite3Step` returns `SQLITE_SCHEMA` (bounded by `SQLITE_MAX_SCHEMA_RETRY`), calling `sqlite3Reprepare(v)` → `sqlite3LockAndPrepare` on the saved SQL → `sqlite3VdbeSwap` → `sqlite3TransferBindings` → `sqlite3VdbeResetStepResult` → `sqlite3VdbeFinalize` of the throwaway VM, so bound parameters survive recompilation. — [src/vdbeapi.c#L980-L1000](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/vdbeapi.c#L980-L1000) [src/prepare.c#L904-L940](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/prepare.c#L904-L940)
- VDBE entry trace: `sqlite3VdbeExec` asserts `VDBE_RUN_STATE`, takes B-Tree mutexes via `sqlite3VdbeEnter` when `p->lockMask` is non-zero, computes `nProgressLimit` from `db->nProgressOps`, checks `db->u1.isInterrupted` (jumping to `abort_due_to_interrupt`), then enters the opcode loop incrementing `nVmStep` per instruction. — [src/vdbe.c#L902-L1000](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/vdbe.c#L902-L1000)
- CLI startup trace: `main()` → `setvbuf(stderr,…,_IONBF)` → `isatty(0)`/`isatty(1)` to set `stdin_is_interactive`/`stdout_is_console` → `atexit(abnormalExit)` → optional `SQLITE_DEBUG_BREAK` debugger attach → `signal(SIGINT, interrupt_handler)`, `SIGTERM`/`SIGHUP` → `sqlite3_sourceid()` vs `SQLITE_SOURCE_ID` mismatch check that exits 1. — [src/shell.c.in#L14020-L14105](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L14020-L14105)
- `main_init()` runs before any SQLite use and configures the library globally: `sqlite3_config(SQLITE_CONFIG_LOG, shellLog, p)`, `verify_uninitialized()`, `sqlite3_config(SQLITE_CONFIG_URI, 1)` and `sqlite3_config(SQLITE_CONFIG_MULTITHREAD)` — so the CLI runs in multithread (not serialized) mode with URI filenames enabled. — [src/shell.c.in#L13874-L13900](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L13874-L13900)
- REPL trace: `process_input` → `one_input_line` → whitespace/`.`/`#` classification → `do_meta_command` for dot-commands (return code 2 means exit) → otherwise append to `zSql` → `sqlite3_complete` gate → `runOneSqlLine` → `shell_exec` → `sqlite3_prepare_v2`/step loop → QRF render. — [src/shell.c.in#L13473-L13565](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L13473-L13565) [src/shell.c.in#L13354-L13370](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L13354-L13370) [src/shell.c.in#L3807-L3860](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L3807-L3860)
- Startup also sources `~/.sqliterc` through the same `process_input` path unless `-noinit` was given, and exits 1 on error when `bail_on_error` is set — meaning the rc file is executed with full dot-command privileges before the user's first keystroke. — [src/shell.c.in#L13745-L13755](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L13745-L13755)
- Lazy-open trace: the shell does not open a database at startup; every dot-command that needs one calls `open_db(p, 0)` first (over 25 call sites), which is what makes `sqlite3` usable with no arguments and then `.open` later. — [src/shell.c.in#L5069-L5075](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L5069-L5075) [src/shell.c.in#L9976-L11130](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L9976-L11130)
- Commit trace (WAL): `sqlite3BtreeCommitPhaseOne` → `sqlite3PagerCommitPhaseOne` → `pagerFlushOnCommit` check → `sqlite3PcacheDirtyList` → `pagerWalFrames` → `sqlite3PcacheCleanAll`, then `sqlite3BtreeCommitPhaseTwo` → `sqlite3PagerCommitPhaseTwo`. — [src/btree.c#L4343](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/btree.c#L4343) [src/btree.c#L4432](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/btree.c#L4432) [src/pager.c#L6551-L6580](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/pager.c#L6551-L6580) [src/pager.c#L6764](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/pager.c#L6764)
- Commit trace (rollback journal): the same `sqlite3PagerCommitPhaseOne` falls into the non-WAL branch where `syncJournal()` and `pager_write_pagelist()` do the durable work, optionally short-circuited by `SQLITE_ENABLE_BATCH_ATOMIC_WRITE` when the device reports `SQLITE_IOCAP_BATCH_ATOMIC` and no super-journal is involved. — [src/pager.c#L6580-L6620](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/pager.c#L6580-L6620) [src/pager.c#L4340](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/pager.c#L4340) [src/pager.c#L4483](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/pager.c#L4483)

## Testing signals

Testing is TCL-first: 1,195 `.test` scripts in `test/` are executed by `testfixture`, an augmented tclsh built from `src/tclsqlite.c` plus 44 `src/test*.c` harness modules that expose internals (malloc fault injection, VFS shims, thread control, syscall interception) to TCL. `test/testrunner.tcl` parallelizes across cores and drives named suites and permutations; `permutations.test` defines 58 test_suite configurations. `make devtest` — the developers' minimum pre-check-in bar — chains `srctree-check` (generated files up to date) and `sourcetest` before running `testrunner.tcl mdevtest`. Fuzzing is a separate, substantial tier: `fuzzcheck` replays fuzzer corpora stored as SQLite databases, and `ossfuzz.c` is the OSS-Fuzz entry point. No CI configuration lives in the repo; extension suites are colocated with their extensions.
- The test corpus is 1,195 `.test` TCL scripts under `test/`, run by the `testfixture` binary built from `$(TESTFIXTURE_SRC)`; `make smoketest` runs just `./testfixture test/main.test` as the fast sanity check. — [test/main.test](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/test/main.test) [main.mk#L1821](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/main.mk#L1821) [main.mk#L1928-L1930](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/main.mk#L1928-L1930)
- `make devtest` depends on `srctree-check` and `sourcetest`, then runs `test/testrunner.tcl mdevtest`; `test`, `quicktest` and the legacy `fulltest`/`alltest`/`soaktest` targets are aliases onto `devtest` or `releasetest`. — [main.mk#L1868-L1912](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/main.mk#L1868-L1912)
- `tool/srctree-check.tcl` is a guard against stale generated artifacts: it regenerates `autoconf/Makefile.msc` via `tool/mkmsvcmin.tcl` and diffs it, and checks `VERSION` against `autoconf/tea/configure.ac`, exiting non-zero with a suggested fix command. — [tool/srctree-check.tcl#L1-L45](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/srctree-check.tcl#L1-L45)
- `test/testrunner.tcl` bootstraps its own interpreter: `find_interpreter` tries `package require sqlite3`, falls back to sourcing a local `pkgIndex.tcl`, then to re-execing under `./testfixture`, and finally offers to build the TCL extension — which is why `make tclextension-install` is recommended before testing. — [test/testrunner.tcl#L26-L60](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/test/testrunner.tcl#L26-L60) [main.mk#L1719](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/main.mk#L1719) [AGENTS.md](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/AGENTS.md)
- The runner estimates work per job class with weights `tcl=1`, `fuzz=22`, `bld=66`, `make=102` (optionally overridden by `test/testrunner_estwork.tcl`) so parallel scheduling packs long builds first. — [test/testrunner.tcl#L11-L21](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/test/testrunner.tcl#L11-L21)
- `test/testrunner_data.tcl` is the declarative test matrix: `trd_builds`, `trd_configs`, `trd_extras`, `trd_all_configs`, `trd_fuzztest_data` and `trd_buildscript` define per-platform build configurations and which suites each one runs, mirroring the old `all.test`. — [test/testrunner_data.tcl#L72-L90](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/test/testrunner_data.tcl#L72-L90) [test/testrunner_data.tcl#L372-L470](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/test/testrunner_data.tcl#L372-L470)
- `test/permutations.test` defines 58 `test_suite` permutations, letting the same `.test` files be re-run under different pragma/compile configurations (this is also what `make valgrindtest` invokes with the `valgrind` permutation). — [test/permutations.test](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/test/permutations.test) [main.mk#L1920-L1922](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/main.mk#L1920-L1922)
- 44 `src/test*.c` modules expose internals to TCL for white-box testing, including `test_malloc.c` (allocation fault injection), `test_vfs.c`/`test_devsym.c`/`test_demovfs.c` (VFS simulation), `test_journal.c`, `test_syscall.c` (syscall interception), `test_thread.c`, `test_mutex.c` and `test_pcache.c`. — [src/test_malloc.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/test_malloc.c) [src/test_vfs.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/test_vfs.c) [src/test_syscall.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/test_syscall.c) [src/test_thread.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/test_thread.c) [src/test1.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/test1.c)
- `test/fuzzcheck.c` replays fuzzer output stored in SQLite databases with `db(dbid, dbcontent)` and `xsql(sqlid, sqltext)` tables, looking only for crashes, assertion faults and leaks — it explicitly does not verify output; eight `fuzzdata*.db` corpora ship in-tree. — [test/fuzzcheck.c#L12-L50](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/test/fuzzcheck.c#L12-L50) [test/fuzzdata1.db](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/test/fuzzdata1.db) [test/fuzzdata8.db](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/test/fuzzdata8.db) [main.mk#L1840](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/main.mk#L1840)
- `test/ossfuzz.c` is the Google OSS-Fuzz `LLVMFuzzerTestOneInput` harness with debug flags (`FUZZ_SQL_TRACE`, `FUZZ_SHOW_MAX_DELAY`, `FUZZ_SHOW_ERRORS`) that can be driven interactively through `test/ossshell.c`. — [test/ossfuzz.c#L1-L35](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/test/ossfuzz.c#L1-L35) [test/ossshell.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/test/ossshell.c)
- Additional specialized fuzzers exist for distinct attack surfaces: `test/dbfuzz.c` and `test/dbfuzz2.c` (database file images), `test/sessionfuzz.c` (changeset blobs), `test/optfuzz.c` (query optimizer equivalence), and `test/fuzzinvariants.c` (result invariants). — [test/dbfuzz2.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/test/dbfuzz2.c) [test/sessionfuzz.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/test/sessionfuzz.c) [test/optfuzz.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/test/optfuzz.c) [test/fuzzinvariants.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/test/fuzzinvariants.c)
- Extension test suites live beside their extensions rather than in `test/`: 149 files under `ext/fts5/test`, 44 `.test` files in `ext/session/`, 43 in `ext/rbu/`, 27 in `ext/rtree/`, 15 in `ext/recover/`, and 5 in `ext/intck/`. — [ext/fts5/test](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/fts5/test) [ext/session/sqlite3session.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/session/sqlite3session.c) [ext/rbu](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/rbu) [ext/recover/recovercorrupt.test](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/recover/recovercorrupt.test) [ext/intck/intck1.test](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/intck/intck1.test)
- Multi-process concurrency is tested by a separate harness, `mptest/mptest.c` with `config01.test`, `config02.test`, `crash01.test`, `crash02.subtest` and `multiwrite01.test`, exercising cross-process locking that single-process TCL tests cannot reach. — [mptest/mptest.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/mptest/mptest.c) [mptest/crash01.test](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/mptest/crash01.test) [mptest/multiwrite01.test](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/mptest/multiwrite01.test)
- Failure triage is documented and tooled: `test/testrunner.tcl errors` and `status` targets are wired into `main.mk`, and AGENTS.md instructs checking `grep '!' testrunner.log`. — [main.mk#L1878-L1886](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/main.mk#L1878-L1886) [doc/testrunner.md#L1-L40](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/doc/testrunner.md#L1-L40) [AGENTS.md](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/AGENTS.md)
- No in-repo CI exists — there is no `.github/`, `.gitlab-ci.yml`, or `.travis.yml` — so coverage of the release matrix (`releasetest`, valgrind, MSVC via `tool/build-all-msvc.bat`, `tool/omittest.tcl` for OMIT-flag combinations) depends on developers running it locally. — [main.mk#L1902-L1906](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/main.mk#L1902-L1906) [tool/build-all-msvc.bat](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/build-all-msvc.bat) [tool/omittest.tcl](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/omittest.tcl) [.fossil-settings/ignore-glob](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/.fossil-settings/ignore-glob)

## Risk map

The core library is one of the most heavily tested C codebases in existence, so the interesting risk is not 'is this correct' but 'where does trust boundary crossing happen'. The sharpest edges are: the CLI, which by design shells out and touches the filesystem; `sqlite3_load_extension`, which `dlopen`s attacker-suppliable paths; the schema itself, which is executable input (the `trusted-schema`/`defensive` model exists precisely because of this); and `sqlite3_rsync`, which `fork`/`execl`s a shell. Structurally, the blast radius is concentrated in a handful of enormous files — `btree.c`, `select.c`, `vdbe.c`, `pager.c`, `where.c` are each 300–400KB — and in generated-file drift, which `srctree-check` only partially guards. Note that AGENTS.md explicitly states the project does not accept agentic code, which is itself a process constraint on any change made here.
- The shell has an explicit unsafe-operation surface gated only by `bSafeMode`: `failIfSafeMode()` guards `.archive`, `.cd`, `.clone`, `.import`, `.load`, `.read`, `.restore` and shell-out, and `safeModeAuth()` blocks the functions `edit`, `fts3_tokenizer`, `load_extension`, `readfile`, `realpath`, `writefile`, `zipfile`, `zipfile_cds` plus `ATTACH`. — [src/shell.c.in#L2366-L2375](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L2366-L2375) [src/shell.c.in#L2789-L2832](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L2789-L2832) [src/shell.c.in#L10038-L11612](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L10038-L11612)
- Safe mode is implemented as an authorizer callback, so it is only active when `SQLITE_OMIT_AUTHORIZATION` is not defined — the whole `safeModeAuth`/`shellAuth` block is inside `#ifndef SQLITE_OMIT_AUTHORIZATION`, meaning a build without the authorizer silently loses these protections. — [src/shell.c.in#L2785-L2875](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L2785-L2875)
- The CLI calls `system()` directly in at least two places (the `edit()` SQL function at `src/shell.c.in:2505` and the `.shell`/`.system` dot-command at `:6045`) and `sqlite3_popen()` in three more (`.import` from a pipe, output redirection to a pipe, and `.read` from a pipe), all constructing command strings from user input. — [src/shell.c.in#L2435-L2510](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L2435-L2510) [src/shell.c.in#L6040-L6050](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L6040-L6050) [src/shell.c.in#L8367](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L8367) [src/shell.c.in#L9553](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L9553) [src/shell.c.in#L11572](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L11572)
- `open_db()` unconditionally calls `sqlite3_enable_load_extension(p->db, 1)` on every CLI connection, re-enabling a capability the library deliberately disables by default; the `.load` dot-command is then only stopped by safe mode. — [src/shell.c.in#L5153-L5156](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L5153-L5156) [src/loadext.c#L592-L604](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/loadext.c#L592-L604) [src/shell.c.in#L11119](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L11119)
- `sqlite3LoadExtension()` passes the caller-supplied path to `sqlite3OsDlOpen` and, on failure, retries with platform suffixes (`.so`/`.dylib`/`.dll`) appended — the only guards are the `SQLITE_LoadExtension` flag, a zero-length-name rejection (to prevent linking the running binary), and a `SQLITE_MAX_PATHLEN` cap added because some `dlopen()` implementations segfault on oversize names. — [src/loadext.c#L561-L632](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/loadext.c#L561-L632)
- The schema is an execution surface: `doc/trusted-schema.md` documents that an attacker who modifies a database's schema (swapping a table for a view, adding triggers, CHECK constraints, generated columns or index expressions) can get code to run in a high-privilege reader's process, which is why functions carry Innocuous/Normal/Direct-Only risk levels and `TRUSTED_SCHEMA` defaults to *on* for backwards compatibility. — [doc/trusted-schema.md#L1-L50](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/doc/trusted-schema.md#L1-L50) [src/main.c#L1013-L1022](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/main.c#L1013-L1022)
- The CLI ties both hardening knobs to one flag: `open_db` sets `SQLITE_DBCONFIG_TRUSTED_SCHEMA` to the value of `--unsafe-testing` and `SQLITE_DBCONFIG_DEFENSIVE` to its inverse, so enabling testing mode disables defensive mode in the same breath. — [src/shell.c.in#L5147-L5152](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L5147-L5152)
- `ext/misc/fileio.c` provides `readfile()`/`writefile()` SQL functions that do arbitrary filesystem I/O; they are registered with `SQLITE_DIRECTONLY` (blocking use from triggers/views/schema) but are plain callable functions from top-level SQL, and the shell compiles them in by default. — [ext/misc/fileio.c#L264](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/misc/fileio.c#L264) [ext/misc/fileio.c#L538](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/misc/fileio.c#L538) [ext/misc/fileio.c#L1275-L1281](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/misc/fileio.c#L1275-L1281) [src/shell.c.in#L5173](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L5173)
- `tool/sqlite3_rsync.c` embeds a `popen2()` implementation copied from Fossil that `fork()`s and `execl()`s either the command directly or `/bin/sh -c zCmd`, building the command from a user-supplied `--ssh` program name and a `USER@HOST:PATH` argument — a shell-injection-shaped surface in a network-facing tool. — [tool/sqlite3_rsync.c#L106-L354](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/sqlite3_rsync.c#L106-L354) [tool/sqlite3_rsync.c#L2077-L2300](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/sqlite3_rsync.c#L2077-L2300)
- Blast radius is concentrated in five files that dominate the tree: `btree.c` (408KB), `select.c` (337KB), `vdbe.c` (325KB), `pager.c` (305KB), `where.c` (298KB) — any edit in these touches the hot path for essentially every query. — [src/btree.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/btree.c) [src/select.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/select.c) [src/vdbe.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/vdbe.c) [src/pager.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/pager.c) [src/where.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/where.c)
- Generated files are a standing hazard: `sqlite3.h`, `parse.c`/`parse.h`, `opcodes.h`/`opcodes.c`, `keywordhash.h`, `pragma.h` and `sqlite3.c` must never be hand-edited, and `tool/srctree-check.tcl` only verifies two things (Makefile.msc sync and VERSION vs tea/configure.ac) — it does not detect a hand-edited `pragma.h` or `parse.c`. — [AGENTS.md](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/AGENTS.md) [tool/srctree-check.tcl#L1-L45](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/srctree-check.tcl#L1-L45) [tool/mkpragmatab.tcl#L1-L20](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/mkpragmatab.tcl#L1-L20)
- Opcode numbering is implicitly coupled to source formatting: `tool/mkopcodeh.tcl` derives opcode numbers by scanning `src/vdbe.c` for lines beginning with `case OP_`, so a reformatting or reordering of those 190 case labels silently renumbers the bytecode. — [src/vdbe.c#L1080-L1090](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/vdbe.c#L1080-L1090) [tool/mkopcodeh.tcl](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/mkopcodeh.tcl) [AGENTS.md](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/AGENTS.md)
- The unix VFS carries a large matrix of platform-conditional locking styles (`posixIoFinder`, `dotlockIoFinder`, `flockIoFinder`, `semIoFinder`, `afpIoFinder`, `nfsIoFinder`, `proxyIoFinder`, `vxworksIoFinder`) selected by `autolockIoFinder`; most of these paths cannot be exercised on any single developer machine. — [src/os_unix.c#L5842-L5945](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/os_unix.c#L5842-L5945) [src/os_unix.c#L8497-L8536](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/os_unix.c#L8497-L8536)
- The shell reads and executes `~/.sqliterc` through `process_input` at startup unless `-noinit` is passed, so a writable home directory is a code-execution vector into any subsequent `sqlite3` invocation. — [src/shell.c.in#L13745-L13755](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L13745-L13755)
- There is a process risk distinct from a code risk: AGENTS.md states SQLite does not accept agentic code and does not accept pull requests without prior legal agreement, because a copyrightable contribution would break the public-domain status of the whole tree. — [AGENTS.md](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/AGENTS.md) [README.md#L44-L56](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/README.md#L44-L56) [LICENSE.md](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/LICENSE.md)
- `main_init()` puts the CLI in `SQLITE_CONFIG_MULTITHREAD` rather than serialized mode, so the shell's own connection is not safe to share across threads — relevant for anyone embedding or extending `shell.c.in`. (inferred) — [src/shell.c.in#L13878-L13884](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L13878-L13884)

## Extension points

SQLite is built almost entirely out of registries, which is why it has such a large third-party ecosystem. At the C level there are seven pluggable interfaces: VFS, virtual-table modules, scalar/aggregate/window functions, collations, page cache, memory allocator, and mutex implementation — plus auto-extensions that fire on every new connection. Above that, FTS5 has its own nested registry for tokenizers and ranking functions. On the source-tree side, the extension points are code generators: adding a PRAGMA means editing `tool/mkpragmatab.tcl`, adding an opcode means adding a `case OP_` in `vdbe.c`, adding grammar means editing `parse.y`, and adding a CLI dot-command means editing the `do_meta_command` chain in `shell.c.in`.
- VFS registry: `sqlite3_vfs_register()`/`sqlite3_vfs_unregister()`/`sqlite3_vfs_find()` form the OS-abstraction plug point, used in-tree by `memdb.c` (the `memdb` VFS) and `os_kv.c` (`kvvfs`), and exported to loadable extensions through the `sqlite3_api_routines` thunk in `loadext.c`. — [src/loadext.c#L320](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/loadext.c#L320) [src/memdb.c#L935](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/memdb.c#L935) [src/os_kv.c#L1086-L1095](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/os_kv.c#L1086-L1095)
- Virtual-table registry: `sqlite3_create_module()` and `sqlite3_create_module_v2()` in `src/vtab.c:108-130` register a `sqlite3_module` vtable implementation; this is how `series`, `zipfile`, `dbstat`, `dbpage`, FTS and R-Tree all attach. — [src/vtab.c#L84-L130](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/vtab.c#L84-L130) [ext/misc/series.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/misc/series.c) [src/dbstat.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/dbstat.c)
- Function registry: built-ins are installed by `sqlite3RegisterBuiltinFunctions()` (`src/func.c:3368`) from a static `FUNCTION(...)` macro table, and the same mechanism is exposed publicly as `sqlite3_create_function*` — extensions like `decimal.c`, `base85.c` and `shathree.c` use it exclusively. — [src/func.c#L3368](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/func.c#L3368) [ext/misc/decimal.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/misc/decimal.c) [ext/misc/shathree.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/misc/shathree.c)
- Collation registry: `createCollation()` (`src/main.c:2907`) backs `sqlite3_create_collation*`; SQLite seeds four built-ins — BINARY in UTF8/UTF16BE/UTF16LE, plus NOCASE and RTRIM — at connection open. — [src/main.c#L2907](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/main.c#L2907) [src/main.c#L3579-L3587](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/main.c#L3579-L3587)
- Auto-extension registry: `sqlite3_auto_extension()` appends to the process-global `sqlite3Autoext` list guarded by `SQLITE_MUTEX_STATIC_MAIN`, and `sqlite3AutoLoadExtensions()` replays it on every new connection. — [src/loadext.c#L800-L830](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/loadext.c#L800-L830) [src/loadext.c#L911](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/loadext.c#L911)
- Loadable-extension ABI: `sqlite3LoadExtension` looks for `sqlite3_extension_init`, and if absent derives a name of the form `sqlite3_X_init` from the filename between the last `/` and the first `.`, lowercasing alphabetic characters — this is the convention every `ext/misc/*.c` file follows. — [src/loadext.c#L605-L640](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/loadext.c#L605-L640) [ext/misc/fileio.c#L1270](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/misc/fileio.c#L1270)
- FTS5 exposes a second-level registry through `fts5_api`: `xCreateTokenizer`, `xCreateTokenizer_v2` (for custom text segmentation) and `xCreateFunction` (for auxiliary/ranking functions receiving an `Fts5ExtensionApi`). — [ext/fts5/fts5.h#L350-L360](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/fts5/fts5.h#L350-L360) [ext/fts5/fts5.h#L696-L735](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/fts5/fts5.h#L696-L735)
- Pluggable subsystem hooks are set through `sqlite3_config()` (`src/main.c:443`), which accepts `SQLITE_CONFIG_MALLOC`, `SQLITE_CONFIG_PAGECACHE`, `SQLITE_CONFIG_MUTEX`, `SQLITE_CONFIG_LOG`, `SQLITE_CONFIG_URI` and threading modes — the CLI itself uses the LOG, URI and MULTITHREAD forms. — [src/main.c#L443](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/main.c#L443) [src/shell.c.in#L13878-L13884](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L13878-L13884)
- PRAGMA extension point: new pragmas are declared as `NAME:`/`TYPE:`/`ARG:`/`IF:` records in the `pragma_def` block of `tool/mkpragmatab.tcl`, which regenerates `pragma.h`; the matching `case PragTyp_XXXXX:` is then added in `src/pragma.c`. — [tool/mkpragmatab.tcl#L1-L50](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/mkpragmatab.tcl#L1-L50) [src/pragma.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/pragma.c) [AGENTS.md](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/AGENTS.md)
- Grammar extension point: SQL syntax changes go in `src/parse.y` (2,169 lines), compiled by the in-tree Lemon generator `tool/lemon.c` against the `tool/lempar.c` template — never by editing `parse.c`. — [src/parse.y](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/parse.y) [tool/lemon.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/lemon.c) [tool/lempar.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/lempar.c) [README.md#L252-L262](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/README.md#L252-L262)
- Shell extension point: `src/shell.c.in` supports an `SQLITE_SHELL_EXTFUNCS` preprocessing hook in `open_db()` for downstream builds to register their own functions, alongside the `INCLUDE ../ext/...` mechanism processed by `tool/mkshellc.tcl`. — [src/shell.c.in#L5183-L5190](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L5183-L5190) [src/shell.c.in#L259-L326](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L259-L326) [tool/mkshellc.tcl](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/mkshellc.tcl)
- Authorizer hook: `sqlite3_set_authorizer()` (`src/auth.c:70`) installs a callback consulted by `sqlite3AuthCheck`/`sqlite3AuthRead` at code-generation time — `sqlite3Select` calls `sqlite3AuthCheck(pParse, SQLITE_SELECT, …)` before compiling any query — which is the hook the shell's `.auth` and safe mode both build on. — [src/auth.c#L70-L250](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/auth.c#L70-L250) [src/select.c#L7710](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/select.c#L7710) [src/shell.c.in#L2838-L2875](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L2838-L2875)
- Build-system extension point: `--amalgamation-extra-src` is threaded through `auto.def` into `AMALGAMATION_EXTRA_SRC`, letting downstream builds fold additional C files into the generated `sqlite3.c`. — [auto.def#L46-L48](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/auto.def#L46-L48) [main.mk#L1145-L1150](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/main.mk#L1145-L1150) [tool/mksqlite3c.tcl#L26-L33](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/mksqlite3c.tcl#L26-L33)
- TCL binding extension point: `Sqlite3_Init` registers the `sqlite3` TCL command via `DbMain`, whose per-database object command `DbObjCmd` is the dispatch table that all 1,195 `.test` scripts drive. — [src/tclsqlite.c#L2485](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/tclsqlite.c#L2485) [src/tclsqlite.c#L4310](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/tclsqlite.c#L4310) [src/tclsqlite.c#L4499-L4513](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/tclsqlite.c#L4499-L4513)

## Contributor handoff

The hard constraints here are unusual and worth internalizing before touching anything: this is public-domain C with no license headers ever added, it is developed in Fossil (the Git remote is a mirror with different check-in names), and AGENTS.md states outright that the project does not accept agentic code — agentic *bug reports with reproducible test cases* are welcome, and patches are accepted only as proof-of-concept documentation. Practically, that means the safe posture is: read, reproduce, write a `.test` case, and propose rather than land. When editing is in scope, the rules are C89/C99 only, `sqlite3Malloc` family for all allocation, `i64`/`u32`/`u64` for width-sensitive values, `SQLITE_OK`/`SQLITE_*` return codes, liberal `assert` with `ALWAYS`/`NEVER` for compiler-opaque invariants, and never touching a generated file. Always run at least `make devtest` after any `src/` change.
- Read first, in this order: `AGENTS.md` (project constraints and generated-file table), `README.md` (source tree map and build instructions), `src/sqliteInt.h` (6,031 lines — the master internal header), and `src/sqlite.h.in` (the public API template and the source of the API docs). — [AGENTS.md](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/AGENTS.md) [README.md#L175-L215](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/README.md#L175-L215) [src/sqliteInt.h](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/sqliteInt.h) [src/sqlite.h.in](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/sqlite.h.in)
- Never add a copyright or license header: every file carries the intentional 'May you do good and not evil' blessing comment instead, and adding a header would jeopardize the public-domain status the project depends on. — [AGENTS.md](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/AGENTS.md) [LICENSE.md](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/LICENSE.md) [src/pager.c#L1-L12](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/pager.c#L1-L12) [test/fuzzcheck.c#L1-L10](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/test/fuzzcheck.c#L1-L10)
- Do not hand-edit generated files: `sqlite3.h` (from `tool/mksqlite3h.tcl`), `parse.c`/`parse.h` (lemon on `src/parse.y`), `opcodes.h`/`opcodes.c` (`mkopcodeh.tcl`/`mkopcodec.tcl`), `keywordhash.h` (`tool/mkkeywordhash.c`), `pragma.h` (`tool/mkpragmatab.tcl`), `sqlite3.c` (`tool/mksqlite3c.tcl`). — [AGENTS.md](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/AGENTS.md) [tool/mksqlite3h.tcl](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/mksqlite3h.tcl) [tool/mkkeywordhash.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/mkkeywordhash.c) [tool/mkpragmatab.tcl](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/mkpragmatab.tcl) [tool/mksqlite3c.tcl](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/mksqlite3c.tcl)
- Build for development with `./configure --dev`, which `auto.def` translates into `--all --debug`, amalgamation *off* (so each `src/*.c` compiles separately and errors point at real files), and `CFLAGS=-O0 -g`. — [auto.def#L20-L35](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/auto.def#L20-L35) [README.md#L118-L124](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/README.md#L118-L124)
- The configure script is autosetup, not GNU Autoconf, and must stay JimTCL-compatible — `autosetup/jimsh0.c` is bundled so the tree can configure without a system tclsh. Project-specific procs are prefixed `sqlite-` (in `autosetup/sqlite-config.tcl`), generic ones `proj-` (in `autosetup/proj.tcl`). — [auto.def#L1-L19](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/auto.def#L1-L19) [autosetup/jimsh0.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/autosetup/jimsh0.c) [autosetup/sqlite-config.tcl](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/autosetup/sqlite-config.tcl) [autosetup/proj.tcl](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/autosetup/proj.tcl)
- Tests need TCL: install `tcl-dev`, run `make tclextension-install` before `make devtest`, and note that `testrunner.tcl` will try to re-exec itself under `./testfixture` if `package require sqlite3` fails. — [AGENTS.md](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/AGENTS.md) [main.mk#L1719](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/main.mk#L1719) [test/testrunner.tcl#L26-L60](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/test/testrunner.tcl#L26-L60) [README.md#L128-L136](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/README.md#L128-L136)
- Minimum test bar for any `src/` change is `make devtest` (`srctree-check` + `sourcetest` + `testrunner.tcl mdevtest`); targeted runs use `./testfixture test/<file>.test` or `test/testrunner.tcl fts5%` pattern matching, and failures are found with `grep '!' testrunner.log`. — [main.mk#L1860-L1876](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/main.mk#L1860-L1876) [AGENTS.md](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/AGENTS.md) [doc/testrunner.md#L28-L60](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/doc/testrunner.md#L28-L60)
- Coding conventions to match: C89/C99 only (no C++/VLAs), all allocation through `sqlite3Malloc`/`sqlite3MallocZero`/`sqlite3_malloc64` rather than raw `malloc`, `i64`/`u32`/`u64` instead of bare `long`/`int` for values that can exceed 2G, `SQLITE_OK`-style return codes with `db->mallocFailed` for deferred OOM detection. — [AGENTS.md](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/AGENTS.md) [src/main.c#L3448-L3450](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/main.c#L3448-L3450) [src/prepare.c#L727-L731](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/prepare.c#L727-L731)
- `assert()` is used as executable documentation throughout and is expected in new code; use `ALWAYS(x)`/`NEVER(x)` for conditions the compiler cannot prove — e.g. `ALWAYS(cnt<=SQLITE_MAX_PREPARE_RETRY)` in the prepare retry loop and `NEVER(pPager->errCode)` in commit. — [AGENTS.md](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/AGENTS.md) [src/prepare.c#L883-L886](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/prepare.c#L883-L886) [src/pager.c#L6542](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/pager.c#L6542)
- Requirement-traceability comments matter: `EVIDENCE-OF: R-#####-#####` markers in the sources tie code to numbered statements in the external documentation (e.g. in `sqlite3_prepare_v2`/`_v3`), and `testcase()` markers mark branches the test suite is expected to cover — preserve both when editing. — [src/prepare.c#L957-L963](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/prepare.c#L957-L963) [src/prepare.c#L975-L982](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/prepare.c#L975-L982) [src/vdbe.c#L952](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/vdbe.c#L952)
- Match the file's existing idiom: this codebase uses two-space indentation, `if( cond ){` spacing with no space after `if`, `/* ... */` block comments only, and `**` comment continuation banners — deviating is immediately visible in diffs. — [src/pager.c#L6527-L6560](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/pager.c#L6527-L6560) [src/vdbeapi.c#L838-L870](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/vdbeapi.c#L838-L870)
- Safe edit boundaries: `ext/misc/*.c` single-file extensions and `test/*.test` scripts are the lowest-risk places to add code; `src/btree.c`, `src/pager.c`, `src/wal.c`, `src/vdbe.c` and `src/where.c` are the highest-risk and should not be touched without a reproducing test. — [ext/misc/series.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/ext/misc/series.c) [test/main.test](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/test/main.test) [src/btree.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/btree.c) [src/wal.c](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/wal.c) [AGENTS.md](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/AGENTS.md)
- Known trap: the CLI is not built from `src/shell.c` — that file does not exist in the tree. Edit `src/shell.c.in` and let the build's `INCLUDE`-processing step produce `shell.c`. — [src/shell.c.in](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in) [main.mk#L2186](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/main.mk#L2186) [tool/mkshellc.tcl](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/tool/mkshellc.tcl)
- Known trap: when reporting a check-in, use the official Fossil name from `manifest.uuid` (`c9b4695ffae5a3388a49643d6819355851a0fda362cdaf140c59fc934759dcac`), not the Git SHA — the README states these differ for all mirrors. — [manifest.uuid](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/manifest.uuid) [README.md#L16-L30](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/README.md#L16-L30)
- Useful debugging levers already in-tree: `SQLITE_DEBUG_BREAK` env var (shell attaches a debugger), `PRAGMA vdbe_trace`/`vdbe_listing`/`vdbe_eqp` via `SQLITE_VdbeTrace` flags in `sqlite3VdbeExec`, `SQLITE_ParserTrace` in `sqlite3RunParser`, and the `.wheretrace`/`.iotrace` dot-commands. — [src/shell.c.in#L14057-L14078](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/shell.c.in#L14057-L14078) [src/vdbe.c#L962-L985](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/vdbe.c#L962-L985) [src/tokenize.c#L621-L628](https://github.com/sqlite/sqlite/blob/fde3a84dddf35f4c19797c8afad04a44c596f4d8/src/tokenize.c#L621-L628)

Source repository: https://github.com/sqlite/sqlite
Full evidence corpus: https://github.com/Codevetter/codevetter/tree/main/benchmarks/repo-unpacks/sqlite.json

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