529 Site Is Overloaded

Non-standard code used by a few platforms to indicate the site is overloaded and shedding requests.

Status

HTTP/1.1 529 Site Is Overloaded

Details

Category: 5xx
Status: Unofficial (Qualys and other vendors). Not registered with IANA. A server, framework, or CDN convention.
Specification: none, not defined by any RFC
Cacheable: Not cacheable
Response body: Allowed
Retry: Retry after a delay

529 is used by a small number of vendors, notably Qualys SSLLabs, to signal that the service is too busy to accept the request. It is not registered and has no standard meaning.

Treat it exactly as you would a 503: back off and come back later.

Common causes

A service deliberately shedding load during a traffic spike.

How to fix it

As the client

Back off with jitter and retry later. Queue the work rather than hammering the endpoint.

As the server

Return 503 with Retry-After so standard clients handle the condition correctly.

Examples

GET /api/analyze?host=example.com HTTP/1.1
Host: api.ssllabs.com

HTTP/1.1 529 Site is overloaded