Rate Limiting¶

The utkit.api.rate_limit module provides rate limiting utilities for FastAPI applications, built on top of SlowAPI.

Installation¶

slowapi is part of the optional api extras. Install utkit with the api extra:

pip install "utkit[api]"

Or with uv:

uv add "utkit[api]"

Quick start¶

from fastapi import FastAPI, Request
from utkit.api.rate_limit import initialize_rate_limiter, rate_limit_exceeded_handler
from utkit.api.rate_limit.middleware import RateLimitMiddleware
from utkit.api.rate_limit.error import RateLimitExceededError

limiter = initialize_rate_limiter("60/minute")

app = FastAPI()
app.state.limiter = limiter
app.add_exception_handler(RateLimitExceededError, rate_limit_exceeded_handler)
app.add_middleware(RateLimitMiddleware)


@app.get("/ping")
@limiter.limit("10/minute")
async def ping(request: Request):
    return {"message": "pong"}

initialize_rate_limiter¶

Creates a Limiter instance configured to use the client's remote IP address as the rate limit key.

def initialize_rate_limiter(rate_limit_default: str = "100/minute") -> Limiter

Returns: Limiter — a configured SlowAPI Limiter instance.

limiter = initialize_rate_limiter("200/minute")

rate_limit_exceeded_handler¶

A pre-built exception handler that returns a 429 Too Many Requests response when a rate limit is exceeded. Import it and register it directly on your FastAPI app.

app.add_exception_handler(RateLimitExceededError, rate_limit_exceeded_handler)

RateLimitMiddleware¶

ASGI middleware that intercepts rate-limit exceptions raised during request processing. Add it to your FastAPI app via add_middleware.

from utkit.api.rate_limit.middleware import RateLimitMiddleware

app.add_middleware(RateLimitMiddleware)

This is a re-export of slowapi.middleware.SlowAPIMiddleware.

RateLimitExceededError¶

Exception raised when a request exceeds the configured rate limit.

from utkit.api.rate_limit.error import RateLimitExceededError

Use this as the exception type when registering the error handler:

app.add_exception_handler(RateLimitExceededError, rate_limit_exceeded_handler)

This is a re-export of slowapi.errors.RateLimitExceeded.

Rate limit string format¶

SlowAPI accepts human-readable limit strings: