fastapi

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Author repo skills-registry

Interpretation is structured for decision-making; original keeps the upstream SKILL.md unchanged.

Decide Fit First

Core job: > Use when this capability is needed. Validate input, call a service, return output. No business logic. router = APIRouter(prefi…
Best fit: Use it when the task has reusable inputs, steps, and validation criteria rather than a one-off answer.
Avoid forcing it: If the source lacks commands, platform support, or external-service evidence, keep those fields unknown instead of guessing.

Design Intent

Structure: The skill is organized around “Route Handlers Are Thin”, “Dependency Injection”, “Lifespan for Startup and Shutdown”, “Response Model”, showing how the author expects the agent to judge fit, collect context, and produce verifiable output.
Trigger evidence: Prioritize the author’s wording around when to use it, what context to collect, and what output shape to produce.
Evidence boundary: Author text states facts, repository files prove commands and paths, and Fluxly only adds fit, limits, and usage judgment.

How To Use It

Inputs: Provide target material, scope, expected result, forbidden changes, and validation method.
Invocation: Name fastapi directly; if the source includes slash commands, start with the command and then add task context.
Validation: Start small and check whether the result follows “Route Handlers Are Thin / Dependency Injection / Lifespan for Startup and Shutdown” before expanding.

Boundaries And Review

Dependencies: It usually needs no extra API key, so start with a small validation task.
Permissions: Declared permissions include read / write; ask the agent to state file, command, and rollback boundaries before acting.
Quality bar: A useful result names the deliverable, evidence, and next action. Generic prose means the task needs tighter context.

FastAPI Conventions

Route Handlers Are Thin

Validate input, call a service, return output. No business logic.

router = APIRouter(prefix="/sessions", tags=["sessions"])

@router.post("", status_code=201, response_model=SessionResponse)
async def create_session(
    body: CreateSessionRequest,
    service: SessionService = Depends(get_session_service),
) -> SessionResponse:
    return await service.create(body.topic)

Dependency Injection

All dependencies in app/core/dependencies.py. Never instantiate services inside route handlers.

@lru_cache
def get_settings() -> Settings:
    return Settings()

async def get_session_service(
    pool: asyncpg.Pool = Depends(get_db_pool),
    settings: Settings = Depends(get_settings),
) -> SessionService:
    return SessionService(pool=pool, settings=settings)

Lifespan for Startup and Shutdown

@asynccontextmanager
async def lifespan(app: FastAPI):
    app.state.db_pool = await asyncpg.create_pool(settings.database_url)
    yield
    await app.state.db_pool.close()

app = FastAPI(lifespan=lifespan)

Do not use the deprecated @app.on_event("startup").

Response Model

Always declare response_model=SomePydanticModel. Never return raw dicts.

Middleware Order

Correlation ID middleware (outermost)
CORS middleware
Rate limiting middleware
Request logging middleware (innermost)

Global Exception Handlers

@app.exception_handler(SessionNotFoundError)
async def handler(request: Request, exc: SessionNotFoundError):
    return JSONResponse(status_code=404, content={"code": "session_not_found", "message": str(exc)})

Exception Hierarchy

Define in app/core/exceptions.py:

class AppError(Exception):
    """Base exception for all application errors."""

class SessionNotFoundError(AppError): ...
class ReasoningValidationError(AppError):
    def __init__(self, reason: str) -> None:
        self.reason = reason
        super().__init__(reason)
class InvalidEventTypeError(ReasoningValidationError): ...

Services raise domain exceptions; global handlers map them to HTTP — never per-route
Never raise HTTPException inside a service layer
Never swallow exceptions silently with bare except:

Source: cheneeheng/agent-skills — distributed by TomeVault.

Fluxly profile Author and license come from source; runtime, permissions, and network are Fluxly detections or estimates

Fluxly category: AI
Author-declared agents: No explicit declaration found; this is not inferred or tested compatibility
Static check: 88 / 100 · heuristic scan, not runtime safety proof
Author / version / license: @tomevault-io · no license declared
Fluxly token estimate: Lean
Fluxly setup estimate: Plug-and-play
External API key: No requirement detected
Detected OS requirements: Unspecified
Runtime requirements: Python
Detected file/system behavior: Read-only
Write / modify
Detected network behavior: Local-only
Install commands: None (reference only)

Profile is derived at build time from SKILL.md and install vectors. Subject to drift from author intent.

Heads up: 未限定 allowed-tools，默认拥有全部工具权限。

Output preview fastapi.preview

The current SKILL.md does not define a fixed output example.

SKILL.md SKILL.md

# FastAPI Conventions

## Route Handlers Are Thin

Validate input, call a service, return output. No business logic.

```python
router = APIRouter(prefix="/sessions", tags=["sessions"])

@router.post("", status_code=201, response_model=SessionResponse)
async def create_session(
    body: CreateSessionRequest,
    service: SessionService = Depends(get_session_service),
) -> SessionResponse:
    return await service.create(body.topic)
```

## Dependency Injection

All dependencies in `app/core/dependencies.py`. Never instantiate services inside route handlers.

```python
@lru_cache
def get_settings() -> Settings:
    return Settings()

async def get_session_service(
    pool: asyncpg.Pool = Depends(get_db_pool),
    settings: Settings = Depends(get_settings),
) -> SessionService:
    return SessionService(pool=pool, settings=settings)
```

## Lifespan for Startup and Shutdown

```python
@asynccontextmanager
async def lifespan(app: FastAPI):
    app.state.db_pool = await asyncpg.create_pool(settings.database_url)
    yield
    await app.state.db_pool.close()

app = FastAPI(lifespan=lifespan)
```

Do not use the deprecated `@app.on_event("startup")`.

## Response Model

Always declare `response_model=SomePydanticModel`. Never return raw dicts.

## Middleware Order

Register in this order (FastAPI processes in reverse registration order):

1. Correlation ID middleware (outermost)
2. CORS middleware
3. Rate limiting middleware
4. Request logging middleware (innermost)

## Global Exception Handlers

Register domain-to-HTTP mappings once in `app/core/middleware.py`:

```python
@app.exception_handler(SessionNotFoundError)
async def handler(request: Request, exc: SessionNotFoundError):

…

Evidence boundary and execution chain

Author text anchors workflow facts; Fluxly only indexes current sections, terms, files, and commands.

sections -> Route Handlers Are Thin → Dependency Injection → Lifespan for Startup and Shutdown → Response Model → Middleware Order → Global Exception Handlers
terms    -> Validate input, call a service, return output. · All dependencies in app/core/dependencies.py. · Do not use the deprecated @app.onevent("startup"). · Always declare responsemodel=SomePydanticModel. · 1. Correlation ID middleware (outermost) 2. · class SessionNotFoundError(AppError): ... · --- > Source: [cheneeheng/agent-skills](https://github.com/cheneeheng/agent-skills) — distributed by [TomeVault](https://tomevault.io).
files/cmd -> app/core/dependencies.py · @app.onevent("startup") · responsemodel=SomePydanticModel · app/core/middleware.py · app/core/exceptions.py · HTTPException · except:
body sha256 -> 8e4e8239c5c0