HTTP Status Codes: Complete Reference
All HTTP status codes explained — 1xx, 2xx, 3xx, 4xx, 5xx — with causes, solutions, and examples.
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Tags: HTTP status codes reference, HTTP error codes, 404 vs 410 difference
HTTP Status Codes: Complete Reference HTTP status codes are the first signal a server sends about whether a request succeeded. Every developer encounters them daily, but the distinctions between similar codes — 401 vs 403, 301 vs 302, 404 vs 410 — matter for both correctness and SEO. This reference covers all five classes with causes, solutions, and when each code should be used. --- All the tools discussed here are available for free at theproductguy.in — client-side, no sign-up required. Part of the HTTP Debugging Tools Guide — a complete toolkit for diagnosing web requests. --- What is how status codes are structured? Status codes are three-digit integers. The first digit indicates the class: | Class | Range | Meaning | |-------|-------|---------| | Informational | 1xx | The request…
Frequently Asked Questions
What are HTTP status codes?
HTTP status codes are three-digit integers in an HTTP response that indicate the outcome of the request. The first digit defines the class: 1xx is informational, 2xx is success, 3xx is redirection, 4xx is client error, and 5xx is server error. They are defined in RFC 9110.
What is the difference between 301 and 302?
A 301 Moved Permanently tells clients and search engines the resource has moved forever — they should update bookmarks and transfer link equity to the new URL. A 302 Found is a temporary redirect — clients should keep using the original URL for future requests. For SEO, always use 301 for permanent moves.
What does HTTP 429 mean?
HTTP 429 Too Many Requests means the client has sent more requests than the server's rate limit allows. The response typically includes a Retry-After header indicating when the client may try again. Implement exponential backoff in your client when you receive 429 responses.
What is the difference between 401 and 403?
401 Unauthorized means the request lacks valid authentication credentials — the client should authenticate and retry. 403 Forbidden means the server understood the request and the identity is known, but that identity lacks permission. A logged-in user hitting a resource they don't have access to gets a 403, not a 401.
What does 503 Service Unavailable mean?
503 means the server cannot handle the request right now — typically due to overload or planned maintenance. Unlike 500 (which indicates a bug), 503 is expected to be temporary. Clients should respect the Retry-After header if present. Load balancers return 503 when all backend instances are unhealthy.
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