Short answer: filter the table. The reference column tells you which RFC defines the code, and “non-standard” means a proxy invented it — 499 is nginx, 520–527 are Cloudflare.
Reading the classes
- 1xx — the request is being handled; informational only.
- 2xx — it worked; 200, 201 and 204 are the three you will actually use.
- 3xx — somewhere else; the permanent/temporary choice is what matters.
- 4xx — the client must change something: credentials, path, payload.
- 5xx — the server failed; retrying may help, but retrying a 501 never does.
A status is not a diagnosis
A 502 tells you a gateway could not read the upstream response; it does not tell you whether the upstream crashed, was too slow, or spoke the wrong protocol. Read the body and the gateway’s own log. The same goes for 500, which is the server saying “something failed” and nothing more.
Debugging a rejected request? The JSON formatter reads the error payload, and the JWT decoder explains a token that produced a 401.