Plain-language meaning
What HTTP code 503 means
RFC 9110 says HTTP 503 indicates that a server is currently unable to handle a request because of temporary overload or scheduled maintenance. The server may include Retry-After to suggest when to try again. RFC 9110 also notes that the existence of the 503 status does not require a server to use it when overloaded — some servers may simply refuse the connection instead.
Keep the code in its namespace
What this code does—and does not—tell you
503 is described as temporary, but it does not promise when the service will recover. Not every overloaded server uses 503, and the status does not reveal which maintenance or capacity condition applies. When a Retry-After value is present it is only the server's suggestion, not a guarantee that the service will be reachable at that time.
Conservative next step
Where to check next
If a Retry-After value is present, follow it. Otherwise wait before trying again, check the service's status page, or contact its operator if the issue continues.
Primary source
Read the official reference
This explanation is scoped to the linked IETF / RFC Editor material, checked September 28, 2026. The original source takes priority and may change its instructions.
RFC 9110, Section 15.6.4: 503 Service UnavailableSame code system
More HTTP error codes
403 error code: HTTP Forbidden
The HTTP 403 Forbidden status means the server understood the request but refuses to fulfill it; the status alone may not explain why.
Read this code guide HTTP · 429429 error code: too many requests
HTTP 429 Too Many Requests indicates rate limiting: a user sent too many requests in a given amount of time.
Read this code guide HTTP · 500500 error code: internal server error
HTTP 500 Internal Server Error is a general server response for an unexpected condition; it does not name a specific cause.
Read this code guide