Retry-After Header

An HTTP response header that tells the client how long to wait before issuing another request. It is sent with 429 Too Many Requests to indicate rate limit reset time, with 503 Service Unavailable to signal planned maintenance windows, and sometimes with 301 redirects. The header value is either a number of seconds (e.g., Retry-After: 60) or an HTTP-date string. Clients that respect Retry-After avoid unnecessary hammering and are more likely to succeed on the next attempt.