The HTTP 429 Too Many Requests client error response status code indicates the client has sent too many requests in a given amount of time. This mechanism of asking the client to slow down the rate of requests is commonly called "rate limiting".

A Retry-After header may be included to this response to indicate how long a client should wait before making the request again.

Implementations of rate limiting vary; restrictions may be server-wide or per resource. Typically, rate-limiting restrictions are based on a client's IP but can be specific to users or authorized applications if requests are authenticated or contain a cookie.