$ exec status
HTTP Status Code Lookup
Look up any HTTP status code — including the special codes returned by Cloudflare, Nginx, IIS, and AWS load balancers. Each code includes its category, plain-English meaning, and a debugging hint.
output will appear here.
$ cat about.md
HTTP status codes are how a server tells the client the outcome of a request. The first digit groups them into five classes: 1xx informational, 2xx success, 3xx redirection, 4xx client error, and 5xx server error. Within each class, individual codes carry specific semantics defined by RFC 9110 (the consolidated HTTP semantics RFC) plus a long tail of WebDAV, OAuth, and vendor-specific additions.
This lookup covers every IANA-registered code, plus the most useful vendor extensions you’ll see in real-world ops: Cloudflare’s 520–530 series for upstream issues, Nginx’s 444 (no-response close) and 499 (client closed request), IIS’s 451 sub-codes, and AWS Elastic Load Balancer’s 460/463/464. For each code, you get the canonical name, the category, a one-line description, the spec it’s defined in, and — for the codes that frequently cause panic in on-call rotations — a hint about the most common root cause and where to look first.
Beyond debugging, knowing the right status code matters when you’re building an API. Returning 404 when you mean 401 leaks information; returning 200 with an error body breaks every standard client; returning 500 when you mean 422 makes your error indistinguishable from a real outage. The lookup is a quick reference to make sure you’re using the right code in the right situation.
$ ls examples/
504Server-side error — upstream didn’t respond in time.
401Look up both 401 and 403 to see the difference between unauthenticated and forbidden.
521Cloudflare-specific code meaning the origin web server is down.
499Client closed the connection before the server replied — common with aggressive timeouts.
$ man --faq
Q.What does 504 actually mean?
A.Gateway Timeout — a proxy or load balancer in front of the origin gave up waiting for an upstream response. Usually means the backend is slow, deadlocked, or down. Check upstream logs and connection pool saturation first.
Q.What is the difference between 401 and 403?
A.401 Unauthorized means you didn’t prove who you are (missing or invalid credentials). 403 Forbidden means the server knows who you are and is refusing anyway (insufficient permissions).
Q.What is HTTP 418?
A.I’m a teapot — defined in RFC 2324 as an April Fools’ joke and kept alive in jest. Not in the IANA registry but supported by many test suites.
Q.Why does my request return 520 from Cloudflare?
A.520 means Cloudflare got an empty, unknown, or invalid response from the origin. Common causes: origin crashed mid-response, invalid headers, or a long-running query that closed the connection.
Q.Are 1xx codes ever returned to clients?
A.Rarely. 100 Continue is used during large uploads when the client sends Expect: 100-continue. 103 Early Hints is increasingly used by CDNs to send Link preload headers before the final response. Most user-facing apps never see 1xx.