Retry-AfterRetry-After is a response header telling the client when it may retry. It is used during overload/maintenance (503) or rate-limit overruns (429) to prevent reckless retries and give the server time to recover.
The value is either a number of seconds to wait (integer) or an absolute time (HTTP-date) at which retrying becomes acceptable.
Paired with 429 Too Many Requests, it explicitly tells the client how long to wait before the next request. Well-behaved clients and SDKs read this value into their automatic backoff, meaningfully reducing server load.
On 503 Service Unavailable (maintenance/overload), Retry-After nudges crawlers, monitors, and clients to wait quietly for that duration. Use an absolute time (HTTP-date) for planned maintenance and relative seconds for load-based cases.
Some redirects (3xx) can also use it to instruct a delayed move, but by far the most common uses in practice are 429 and 503.
Retry-After: <HTTP-date> | <seconds>e.g. Retry-After: 120