HTTP 501 Not Implemented
The server doesn't support the functionality required to fulfill this request. The right response for a stub endpoint.
What it means
501 is the honest response for "that's a real method, the server just doesn't implement it." Different from 405 (the URL exists but doesn't accept that method) and from 404 (the URL doesn't exist at all). Most production servers don't issue 501s in practice.
If you're seeing 501 from a downstream service, it usually means you're hitting a stubbed or future-feature endpoint that isn't wired up yet.
Common causes
- Method not implemented yet (e.g. PATCH on a service that only supports GET/POST)
- Stub endpoint left in production
- Old client hitting a deprecated method
How to fix it
- 1Use a supported method (check OPTIONS or docs)
- 2Wire up the missing handler if it should exist
How Uptimera reports 501
Uptimera flags 501 as down.
Related codes
Method Not Allowed
The HTTP method (GET, POST, etc.) isn't allowed on this URL. The resource exists; you used the wrong verb.
Internal Server Error
Generic server-side failure. Something blew up that the server didn't have a more specific response for.
Service Unavailable
The server is temporarily unavailable — overloaded, in maintenance, or intentionally not accepting traffic.
Catch 501s before your customers do
Uptimera monitors your URLs from multiple regions and alerts the moment a 501 starts firing. Free plan included.