HTTP Status Code Lookup
Type a status code or a few words and get a clear explanation: what the code means, the usual causes, what to do about it and, where it matters, how search engines treat it. The list covers all registered codes from the HTTP standards plus common unofficial ones from Nginx, Cloudflare, IIS and Laravel, with the specification each comes from.
- Runs in your browser
- No sign-up
- Free to use
How to use HTTP Status Code Lookup
- Type a code such as 503, or words such as “redirect” or “timeout”.
- Or filter by class: 1xx, 2xx, 3xx, 4xx, 5xx or unofficial.
- Open a code to read causes, fixes and SEO notes.
- Link to a code directly by adding #404 (for example) to the page address.
HTTP Status Code Lookup features
About 80 codes
Every registered status code plus common unofficial ones.
Practical advice
Typical causes and fixes, not just definitions.
SEO effects
How search engines treat redirects, errors and maintenance responses.
CDN and server codes
Nginx 444/499 and Cloudflare 520–530 explained.
Fast search
By number, by class pattern such as 4xx, or by words.
Works offline
The reference loads with the page; nothing is fetched.
When to use HTTP Status Code Lookup
- Understanding an error message shown by a website or API.
- Choosing the right status code when building an API.
- Deciding between 301, 302, 307 and 308 for a redirect.
- Diagnosing Cloudflare 52x errors on your own site.
HTTP Status Code Lookup FAQ
What do the first digits mean?
1xx are informational, 2xx mean success, 3xx are redirects, 4xx are client errors (a problem with the request) and 5xx are server errors (the server failed to handle a valid request).
What is the difference between 401 and 403?
401 means you are not authenticated: log in or provide valid credentials. 403 means the server knows or does not need to know who you are and refuses anyway.
Should I use 301 or 302?
Use 301 (or 308) when a URL has moved for good, so search engines transfer the old address’s signals to the new one. Use 302 (or 307) for temporary moves.
What status should a maintenance page return?
503 Service Unavailable, ideally with a Retry-After header. Search engines then retry later instead of treating the pages as gone.
Is 404 bad for SEO?
No, a 404 for a URL that does not exist is correct. Problems arise when important pages return 404, when internal links point to missing pages, or when missing pages return 200 (soft 404).
Why do I see a code that is not in the standard?
Servers and CDNs define their own codes for situations the standard does not cover, such as Cloudflare’s 52x codes for problems between Cloudflare and the origin server. They are listed under Unofficial.
How HTTP status codes work
Every HTTP response starts with a three-digit status code that summarises the outcome of the request. Browsers, crawlers, caches and API clients make decisions based on it: whether to show the body, follow a redirect, retry later, cache the result or report an error. Choosing and interpreting the code correctly is therefore as important as the content of the response itself.
The first digit defines the class, and clients that do not know a particular code fall back to the class. Within each class, specific codes add meaning: 304 tells a cache its copy is still valid, 429 tells a client to slow down, 503 tells a crawler to come back later. The codes are defined mainly in RFC 9110, the current HTTP semantics standard, with extensions such as 429 and 511 in RFC 6585 and WebDAV codes in their own documents.
Redirects are where status codes affect search most directly. Permanent redirects, 301 and 308, tell search engines to replace the old URL with the new one and pass on its signals; temporary ones, 302 and 307, keep the old URL indexed. The difference between 301 and 308, and between 302 and 307, is whether the request method may change from POST to GET when following the redirect.
Error codes split responsibility. A 4xx code says the request was wrong: a missing page, missing credentials, invalid input or too many requests. A 5xx code says the server failed. Gateways and CDNs add their own layer: a 502 or 504 from Nginx or a load balancer means the application behind it failed or was too slow, and Cloudflare’s 52x codes mean the problem lies between Cloudflare and your origin server.
For APIs, precise codes make clients simpler. Return 201 with a Location header after creating something, 204 when there is nothing to return, 400 for malformed requests, 422 for validation errors, 409 for conflicts and 429 with Retry-After for rate limits. Always pair error codes with a readable message in the body, and never expose stack traces or internal details in 500 responses.