from fastapi import FastAPI, Request

app = FastAPI()


@app.middleware("http")
async def add_process_time_header(request: Request, call_next):
    start_time = time.perf_counter()
    response = await call_next(request)
    process_time = time.perf_counter() - start_time
    response.headers["X-Process-Time"] = str(process_time)

```Python hl_lines="10  12-13"
{!../../docs_src/middleware/tutorial001.py!}
```

/// tip

Here we use <a href="https://docs.python.org/3/library/time.html#time.perf_counter" class="external-link" target="_blank">`time.perf_counter()`</a> instead of `time.time()` because it can be more precise for these use cases. 🤓

///

## Other middlewares

* 📝 Add note about `time.perf_counter()` in middlewares. PR [#12095](https://github.com/fastapi/fastapi/pull/12095) by [@tiangolo](https://github.com/tiangolo).
* 📝 Tweak middleware code sample `time.time()` to `time.perf_counter()`. PR [#11957](https://github.com/fastapi/fastapi/pull/11957) by [@domdent](https://github.com/domdent).