fastmcp/docs/python-sdk/fastmcp-server-middleware-rate_limiting.mdx
Jeremiah Lowin 9b248a15b3
Update repository references for transfer to prefecthq (#3207)
* Update repository references from jlowin/fastmcp to prefecthq/fastmcp

* Retrigger CI after repo transfer

* chore: Update SDK documentation

* Only run deep triage on bug issues for jlowin

---------

Co-authored-by: marvin-context-protocol[bot] <225465937+marvin-context-protocol[bot]@users.noreply.github.com>
2026-02-18 10:33:56 -05:00

97 lines
3.2 KiB
Text

---
title: rate_limiting
sidebarTitle: rate_limiting
---
# `fastmcp.server.middleware.rate_limiting`
Rate limiting middleware for protecting FastMCP servers from abuse.
## Classes
### `RateLimitError` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/middleware/rate_limiting.py#L15" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
Error raised when rate limit is exceeded.
### `TokenBucketRateLimiter` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/middleware/rate_limiting.py#L22" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
Token bucket implementation for rate limiting.
**Methods:**
#### `consume` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/middleware/rate_limiting.py#L38" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
```python
consume(self, tokens: int = 1) -> bool
```
Try to consume tokens from the bucket.
**Args:**
- `tokens`: Number of tokens to consume
**Returns:**
- True if tokens were available and consumed, False otherwise
### `SlidingWindowRateLimiter` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/middleware/rate_limiting.py#L61" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
Sliding window rate limiter implementation.
**Methods:**
#### `is_allowed` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/middleware/rate_limiting.py#L76" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
```python
is_allowed(self) -> bool
```
Check if a request is allowed.
### `RateLimitingMiddleware` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/middleware/rate_limiting.py#L92" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
Middleware that implements rate limiting to prevent server abuse.
Uses a token bucket algorithm by default, allowing for burst traffic
while maintaining a sustainable long-term rate.
**Methods:**
#### `on_request` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/middleware/rate_limiting.py#L152" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
```python
on_request(self, context: MiddlewareContext, call_next: CallNext) -> Any
```
Apply rate limiting to requests.
### `SlidingWindowRateLimitingMiddleware` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/middleware/rate_limiting.py#L170" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
Middleware that implements sliding window rate limiting.
Uses a sliding window approach which provides more precise rate limiting
but uses more memory to track individual request timestamps.
**Methods:**
#### `on_request` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/src/fastmcp/server/middleware/rate_limiting.py#L219" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
```python
on_request(self, context: MiddlewareContext, call_next: CallNext) -> Any
```
Apply sliding window rate limiting to requests.