By the numbers

Data collected on 2026-04-30 from the master branch (commit d8a2c1eda).

Codebase size

Area	Python files	Lines of code
Framework (fastapi/)	48	19,335
Tests (tests/)	581	74,543
Doc examples (docs_src/)	454	8,556

The framework is small. The repo is large because tutorials and translations live alongside it. The Markdown content under docs/ totals 1,518 files across 14 languages.

xychart-beta horizontal
    title "Lines of code by area"
    x-axis ["fastapi/", "docs_src/", "tests/"]
    y-axis "Lines"
    bar [19335, 8556, 74543]

Largest source files in fastapi/

File	Lines	What lives there
fastapi/routing.py	4,956	APIRouter, APIRoute, APIWebSocketRoute, request/response wrappers, response serialization
fastapi/applications.py	4,691	The FastAPI class — the entrypoint user code instantiates
fastapi/param_functions.py	2,461	Functional wrappers for Path, Query, Header, Cookie, Body, Form, File, Depends, Security
fastapi/dependencies/utils.py	1,057	solve_dependencies, get_dependant, body-field flattening, request parsing
fastapi/params.py	755	Param, Body, Form, File, Depends, Security FieldInfo subclasses
fastapi/security/oauth2.py	693	OAuth2PasswordBearer, OAuth2AuthorizationCodeBearer, OAuth2PasswordRequestForm, SecurityScopes
fastapi/openapi/utils.py	606	get_openapi() schema generator

These six files carry the bulk of the framework's logic. Everything else is either a thin Starlette/Pydantic shim, a security scheme, or supporting glue.

Tests

• 581 test files; 74,543 lines.
• Three groups: framework unit tests (tests/test_*.py), tutorial replays (tests/test_tutorial/, 77 sub-directories mirroring docs_src/), and benchmarks (tests/benchmarks/).
• The largest single file is tests/test_include_router_defaults_overrides.py at 394,863 lines — it is generated to enumerate router-inclusion cases. The next-largest, tests/test_generate_unique_id_function.py, is 76,760 lines.
• pytest -n auto --dist loadgroup (see scripts/test.sh) parallelises across cores. pyproject.toml enforces filterwarnings = ["error"].

Activity

Window	Commits
Last 90 days	523
2026 (year-to-date)	597
2025	1,144
2024	1,999
2023	780
2022	665
2021	482
2020	725
2019	2,193
All time	7,100

xychart-beta
    title "Commits per year"
    x-axis ["2019", "2020", "2021", "2022", "2023", "2024", "2025", "2026 YTD"]
    y-axis "Commits"
    bar [2193, 725, 482, 665, 780, 1999, 1144, 597]

2024 was the highest-activity year on record, driven heavily by automated maintenance commits.

Bot-attributed commits

Counting authors whose name ends in [bot]:

• 540 commits (≈ 7.6% of all commits) carry an explicit bot author.
• The leading bots in the most recent 200 commits are github-actions[bot] (97) and dependabot[bot] (40). github-actions[bot] runs the release-notes update, sponsor regeneration, contributor refresh, and translation workflows; dependabot[bot] keeps the lockfile current.
• This is a lower bound — AI-assisted edits made by humans through normal commit flows leave no trace in git history.

Cross-cutting

• TODO/FIXME/HACK comments in fastapi/: 15. Almost all are short notes about Pydantic-version edge cases.
• Workspace dependencies (pyproject.toml [project.dependencies]): 5 runtime dependencies (starlette, pydantic, typing-extensions, typing-inspection, annotated-doc). The standard extra adds fastapi-cli, httpx, jinja2, python-multipart, email-validator, uvicorn[standard], pydantic-settings, pydantic-extra-types.
• Optional dependency groups declared in pyproject.toml: 4 (standard, standard-no-fastapi-cloud-cli, all, plus the dev dependency-groups).