HTTP 503 Service Unavailable

The server is temporarily unable to handle the request — overloaded, or down for maintenance. Often accompanied by Retry-After.

Why you would test it

Unlike a 500, a 503 is explicitly retryable. Test that your client treats them differently instead of collapsing both into "error".

Endpoints that return 503

2 endpoints in this playground answer with 503. Every one is free, needs no signup, and can be called from the browser or with curl.

• GET https://funapi.dev/api/protocol/v1/maintenance — Always, with a Retry-After header. Good retry/backoff practice. (Protocol Lab API)
• GET https://funapi.dev/api/faults/v1/target — Configured outage (Fault Injection API)

Other server error codes

• 500 Internal Server Error
• 504 Gateway Timeout

All HTTP status codes · All 37 mock REST APIs · Getting started guide