Look up a status, pick the right one for an API, or hit a live endpoint that actually returns it. Add ?code=418 to this URL and the response is that status — useful for curl, interceptors, and “what does my client do on 503?” Nothing here phones home except the Try it fetch to this same page.
Which class?
A condition in If-Match / If-Unmodified-Since / If-None-Match failed.
When to use
Optimistic concurrency: the ETag did not match, so the write was rejected.
Don’t
General validation is 400/422. Lost updates without conditionals are often 409.
Live URL
curl -i https://corecoding.com/utilities/http-status.php?code=412
No codes match.
Code use cases