Is 423 standard outside WebDAV?

Not really. Most REST APIs use 409 Conflict for locking. 423 is technically valid and somewhat self-documenting if your API has explicit locks.

423 Locked: HTTP Status Code Meaning, Causes, and Fixes

What 423 Locked means

423 Locked is a WebDAV code for resource-level locking. Some non-WebDAV APIs use it to indicate temporary locks on resources during long-running operations (e.g. while a CI job is editing a config file, the file is locked). It is similar to 409 Conflict but specifically about explicit lock state, not state-mismatch in general.

When servers should return it: Return 423 when a resource has an explicit lock that prevents the requested operation.

Example response

HTTP/2 423
content-type: application/json
{"error":"resource locked","unlock_at":"2026-05-05T15:00:00Z"}

More references

For a one-page reference of all HTTP status codes, see the HTTP cheat sheet. For testing API responses, try the API Tester tool. For inspecting responses on the command line, the curl cheat sheet covers the most common flags.