FastAPI¶

The FAPI family checks FastAPI applications across files: which router the app includes, which error codes the OpenAPI schema declares (ADR-037). Every FAPI rule is opt-in, and none reports what Ruff's FAST rules already do. On a new project, inwards init --style fastapi turns them all on as warnings.

Code	Name	What it flags	On
FAPI001	`endpoint-metadata`	A path operation without the OpenAPI metadata the project requires (summary, response model, status code)	opt-in
FAPI002	`undocumented-error-response`	A path operation that can produce an error status code (raised directly, in a helper or dependency, or through an app's exception handler) its `responses=` doesn't declare	opt-in
FAPI003	`router-wiring`	An `APIRouter` with routes that no app includes, routers that include each other in a cycle, or an `include_router` above the included router's routes	opt-in
FAPI005	`route-shadowing`	A path operation that an earlier one with the same method already answers: `/users/{id}` above `/users/me`, or the same method and path twice	opt-in
FAPI006	`lifespan-events`	A deprecated `on_event` handler or `on_startup=` (a warning), and one next to a `lifespan=` that makes FastAPI ignore it (an error)	opt-in
FAPI007	`yield-dependency-swallows`	A dependency with `yield` whose `except` clause around it doesn't re-raise, so the endpoint's error is hidden	opt-in
FAPI008	`duplicate-operation-id`	Two path operations of one app with the same literal `operation_id`	opt-in
FAPI009	`depends-called`	`Depends(get_db())`: the dependency is called at import time instead of being passed	opt-in

The rules index has the rules of every category in one list you can search, filter and sort.