“The API is slow” starts a hunt. Somebody opens the APM dashboard, somebody else greps the load balancer logs, a third person checks whether the database is on fire. An hour later the team has three theories and no measurement. One request, timed phase by phase, answers the first question in under a second: whether the time went to name lookup, the TCP connect, the TLS handshake, the server or the transfer of the body.

The HTTP status code specification is 30 years old, fully documented, and widely misimplemented. The misimplementation is not ignorance — most API developers know that 200 means success and 404 means not found. It is the edge cases where the correct status code requires a moment of thought that the wrong choice gets made, and the wrong choice gets propagated to every consumer who must now handle an error that does not mean what the specification says it means.