fapi-limiter 0.1.0

Flexible rate limiting for FastAPI using pyrate-limiter

fapi-limiter

Flexible rate limiting for FastAPI powered by pyrate-limiter.

This project is being developed with AI assistance (GitHub Copilot), but all code, design decisions, and implementation details are reviewed and validated by the author.

Installation

# pip
pip install fapi-limiter

# uv
uv add fapi-limiter

Usage

Middleware (app-wide)

Apply rate limiting to every request in the application.

from fastapi import FastAPI
from pyrate_limiter import Duration, InMemoryBucket, Limiter, Rate

from fapi_limiter import RateLimiterMiddleware

app = FastAPI()

limiter = Limiter(InMemoryBucket([Rate(10, Duration.MINUTE)]))
app.add_middleware(RateLimiterMiddleware, limiter=limiter)

Dependency (per-route)

Apply rate limiting to specific routes using FastAPI's dependency injection.

from fastapi import Depends, FastAPI
from pyrate_limiter import Duration, InMemoryBucket, Limiter, Rate

from fapi_limiter import RateLimiter

app = FastAPI()

limiter = Limiter(InMemoryBucket([Rate(10, Duration.MINUTE)]))


@app.get("/limited", dependencies=[Depends(RateLimiter(limiter))])
def limited():
    return {"ok": True}

Response Headers

On every request, the following headers are set:

Header	Description
X-RateLimit-Limit	Maximum requests allowed in the window
X-RateLimit-Remaining	Requests remaining in the current window
X-RateLimit-Reset	Unix timestamp (ms) when the window resets

When the limit is exceeded, 429 Too Many Requests is returned and two additional headers are set:

Header	Description
Retry-After	Unix timestamp (ms) after which the client may retry

Configuration

Both RateLimiterMiddleware and RateLimiter accept the same options:

Parameter	Type	Default	Description
limiter	Limiter	required	A pyrate-limiter Limiter instance
callback	CallbackFunction	default_callback	Called when the limit is exceeded
identifier	Callable[[Request], str]	get_default_identifier	Extracts a key from the request (e.g. IP + path)
blocking	bool	False	Whether to block and wait instead of rejecting

RateLimiterMiddleware also accepts:

Parameter	Type	Default	Description
skip	SkipFunction | None	None	If it returns True, the request bypasses rate limiting

Custom Callback

The callback is invoked when a request is rate-limited. It receives the Request and a headers dict, and should raise an HTTPException:

from fastapi import HTTPException, Request
from fapi_limiter import RateLimiterMiddleware

def my_callback(request: Request, headers=None):
    raise HTTPException(status_code=429, detail="Slow down!", headers=headers)

app.add_middleware(RateLimiterMiddleware, limiter=limiter, callback=my_callback)

Custom Identifier

By default the identifier is {client_ip}:{path}. You can override it to key by user, API token, etc.:

def by_user(request: Request) -> str:
    return request.headers.get("X-User-Id", "anonymous") + ":" + request.url.path

app.add_middleware(RateLimiterMiddleware, limiter=limiter, identifier=by_user)

Skip Function

Use skip on RateLimiterMiddleware to bypass rate limiting for certain requests (e.g. health checks):

def skip_health(request: Request) -> bool:
    return request.url.path == "/health"

app.add_middleware(RateLimiterMiddleware, limiter=limiter, skip=skip_health)

Credits

• fastapi-limiter by long2ice

License

MIT