WebCheck marks an HTTP check as failed when the response code falls outside that target’s expected range. The code tells you what the server, proxy or edge service returned; it does not identify the cause by itself.
Access and request errors
401 usually means the route requires authentication; 403 means access was refused; 404 means that path was not found; and 429 means a rate limit was applied. Check whether the path is meant to be public and which layer returned the response.
Server and gateway errors
500 is an application error, 502 is a bad response from an upstream service, 503 means the service is unavailable, and 504 means a gateway timed out waiting for an upstream. A 503 may be intentional during maintenance.
Where to look next
Open the failed run and note its status, final URL, redirects, response timing and any headers WebCheck recorded. Then compare that evidence with application, proxy and CDN logs around the same time.