> ## Documentation Index
> Fetch the complete documentation index at: https://docs.fact0.io/llms.txt
> Use this file to discover all available pages before exploring further.

# FastAPI

> Audit logging middleware and lifespan hooks for FastAPI services.

# FastAPI

## Install

```bash theme={null}
pip install fact0-sdk fastapi
```

## Async client with lifespan

```python theme={null}
from contextlib import asynccontextmanager
from fastapi import FastAPI
import fact0

audit: fact0.AsyncClient | None = None

@asynccontextmanager
async def lifespan(app: FastAPI):
    global audit
    audit = fact0.AsyncClient(api_key="f0_live_...")
    yield
    await audit.close()

app = FastAPI(lifespan=lifespan)
```

## Request-level audit middleware

```python theme={null}
from fact0.integrations.fastapi import AuditMiddleware

app.add_middleware(
    AuditMiddleware,
    client_factory=lambda: audit,
    action_prefix="api",
)
```

The middleware logs `api.request` on each request with method, path, status, and duration in metadata.

## Manual instrumentation

```python theme={null}
@app.post("/approve/{invoice_id}")
async def approve(invoice_id: str, user: User = Depends(get_user)):
    await audit.audit.log(
        actor={"id": user.id, "type": "human"},
        action="invoice.approve",
        resource={"id": invoice_id, "type": "invoice"},
        outcome="success",
    )
    ...
```

Use the same `resource.id` (often an execution ID) across all steps of one agent run for correlated filtering.

## Related

* [Async client](/sdk/python/async) - batching, drain semantics, retries
* [Audit client reference](/sdk/python/audit)