HTTP Status Code Lookup
Look up any HTTP status code (1xx–5xx) to see its official name, meaning, common causes, and how to fix it. Covers all 60+ standard status codes with practical explanations for developers.
59 status codes
How to Use HTTP Status Code Lookup
- 1Enter any HTTP status code (e.g., 404, 500, 301) or search by keyword.
- 2The official status reason phrase and full description are shown.
- 3Common causes and recommended fixes are provided for each error code.
- 4Browse all codes by category: 1xx Informational, 2xx Success, 3xx Redirect, 4xx Client Error, 5xx Server Error.
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Frequently Asked Questions
What is the difference between 401 and 403?▾
401 Unauthorized means the request lacks valid authentication — you're not logged in or your credentials are invalid. The server is saying "who are you?" 403 Forbidden means the server knows who you are (authenticated) but you don't have permission to access this resource. The server is saying "I know who you are, but you can't access this." A common mistake: returning 401 for "not logged in" and 403 for "logged in but no permission". Always return 401 with a WWW-Authenticate header to indicate that credentials will help.
What is the difference between 301 and 302?▾
301 Moved Permanently tells clients and search engines that the resource has permanently moved — update your bookmarks. Search engines transfer SEO ranking (link equity) to the new URL. 302 Found (temporary) tells clients to fetch this request from the new URL but keep using the original URL for future requests. Search engines do not transfer full SEO equity for 302s. Use 301 for permanent URL changes (HTTPS migration, domain change). Use 302 for A/B testing, temporary maintenance pages, or login redirects.
Why does 404 differ from 410?▾
404 Not Found means the resource cannot be found — it may have existed or may not have. The client should retry in the future. 410 Gone explicitly communicates that the resource was deliberately removed and will not be available again. 410 is better for SEO when permanently removing content — Googlebot will de-index 410 pages faster than 404 pages. Use 410 for deleted blog posts, discontinued products, or closed accounts when you want to signal permanent removal.
What causes 502 vs 503 vs 504?▾
502 Bad Gateway: Your proxy/load balancer received an invalid response from the backend app server (e.g., app crashed, returned garbage). 503 Service Unavailable: The backend app is up but refusing connections — typically overloaded, in maintenance mode, or out of connections. 504 Gateway Timeout: The proxy waited too long for the backend to respond — the backend is running but too slow (e.g., slow database query). Common fixes: 502=restart app server; 503=reduce load or wait for maintenance; 504=optimize slow queries or increase timeout.
When should I use 422 vs 400?▾
400 Bad Request is for syntactic errors — the request itself is malformed (invalid JSON, wrong content-type, missing required headers). 422 Unprocessable Content (formerly Unprocessable Entity) is for semantic validation errors — the request format is correct but the data fails business validation (email format invalid, age is negative, username already taken). Modern REST APIs prefer 422 for validation errors with a structured body listing each field error. Rails uses 422 by default for form validation failures. GraphQL APIs typically return 200 with errors in the response body.