# SiteError.com > A free, human-friendly reference for every HTTP status code — standard 1xx through 5xx plus vendor-specific codes from NGINX, Cloudflare, AWS, and Microsoft IIS. Each code page has a plain-English explanation, the official RFC quote, a real example HTTP response, code snippets, SEO guidance, and links to commonly confused codes. SiteError.com covers 81 HTTP status codes in total. Every code page includes: official name, category, plain-English and playful descriptions, common causes, a real HTTP response example, RFC references, SEO/indexing notes, code snippets in multiple languages, and cross-links to related and commonly confused codes. The site also offers interactive tools for comparing codes, testing real HTTP responses, and learning through a quiz. ## Featured HTTP status codes - [200 OK](https://siteerror.com/code/200): The request succeeded. The meaning of success depends on the HTTP method used. - [301 Moved Permanently](https://siteerror.com/code/301): The URL of the requested resource has been changed permanently. The new URL is given in the response. - [302 Found](https://siteerror.com/code/302): The URI of the requested resource has been changed temporarily. - [304 Not Modified](https://siteerror.com/code/304): Indicates that the resource has not been modified since the version specified in the request headers. - [400 Bad Request](https://siteerror.com/code/400): The server cannot process the request due to client error (malformed syntax, invalid request framing, etc.). - [401 Unauthorized](https://siteerror.com/code/401): The client must authenticate itself to get the requested response. - [403 Forbidden](https://siteerror.com/code/403): The client does not have access rights to the content. - [404 Not Found](https://siteerror.com/code/404): The server cannot find the requested resource. The URL is not recognized. - [418 I'm a Teapot](https://siteerror.com/code/418): The server refuses the attempt to brew coffee with a teapot. An April Fools' joke from 1998. - [429 Too Many Requests](https://siteerror.com/code/429): The user has sent too many requests in a given amount of time (rate limiting). - [500 Internal Server Error](https://siteerror.com/code/500): The server has encountered a situation it doesn't know how to handle. - [502 Bad Gateway](https://siteerror.com/code/502): The server was acting as a gateway and received an invalid response from the upstream server. - [503 Service Unavailable](https://siteerror.com/code/503): The server is not ready to handle the request, often due to maintenance or overloading. - [504 Gateway Timeout](https://siteerror.com/code/504): The server was acting as a gateway and could not get a response in time. ## HTTP status code categories - [1xx Informational](https://siteerror.com/category/1xx): 4 codes — 100, 101, 102, 103 - [2xx Success](https://siteerror.com/category/2xx): 10 codes — 200, 201, 202, 203, 204, 205, 206, 207, 208, 226 - [3xx Redirection](https://siteerror.com/category/3xx): 8 codes — 300, 301, 302, 303, 304, 305, 307, 308 - [4xx Client Error](https://siteerror.com/category/4xx): 29 codes — 400, 401, 402, 403, 404, 405, 406, 407, 408, 409, 410, 411, 412, 413, 414, 415, 416, 417, 418, 421, 422, 423, 424, 425, 426, 428, 429, 431, 451 - [5xx Server Error](https://siteerror.com/category/5xx): 11 codes — 500, 501, 502, 503, 504, 505, 506, 507, 508, 510, 511 ## Vendor-specific status codes - [NGINX](https://siteerror.com/category/nginx): 5 codes — 495, 496, 497, 498, 499 - [Cloudflare](https://siteerror.com/category/cloudflare): 8 codes — 520, 521, 522, 523, 524, 525, 526, 527 - [AWS ELB](https://siteerror.com/category/aws): 3 codes — 460, 463, 561 - [Microsoft IIS](https://siteerror.com/category/iis): 2 codes — 440, 449 ## Tools - [Compare status codes](https://siteerror.com/compare): Side-by-side comparison of two or more codes, including commonly confused pairs like 401 vs 403 and 502 vs 504. - [Cheat sheet](https://siteerror.com/cheat-sheet): Printable quick reference of every HTTP status code grouped by category. - [Quiz](https://siteerror.com/quiz): Interactive quiz to test your knowledge of HTTP status codes. - [API playground](https://siteerror.com/api-playground): Send a request and inspect the real HTTP response, headers, and status code. - [URL checker](https://siteerror.com/check): Check the actual HTTP status a URL returns, including redirect chains, using different user agents. ## Articles - [Understanding HTTP 301 Redirects: SEO, Migrations, and Common Pitfalls](https://siteerror.com/blog/understanding-301-redirects): A comprehensive guide to HTTP 301 Moved Permanently — when to use it, how it affects SEO, implementation examples, and mistakes that can tank your rankings. - [Understanding 429 Too Many Requests: Rate Limiting Done Right](https://siteerror.com/blog/understanding-429-too-many-requests): A deep dive into HTTP 429 Too Many Requests — why rate limiting matters, how to implement it on the server, and how to handle it gracefully as a client. - [Understanding HTTP 200 OK: The Success Status Code Explained](https://siteerror.com/blog/understanding-200-ok): A comprehensive guide to the HTTP 200 OK status code — what it means, how it varies by HTTP method, common pitfalls, and best practices for API design. - [Understanding 500 Internal Server Error: Causes, Debugging, and Prevention](https://siteerror.com/blog/understanding-500-errors): A deep dive into HTTP 500 Internal Server Error — what triggers it, how to debug it, and strategies to prevent unhandled server failures in production. - [Understanding 502 Bad Gateway Errors: Causes, Fixes, and Prevention](https://siteerror.com/blog/understanding-502-errors): A deep dive into HTTP 502 Bad Gateway errors — what causes them, how to diagnose them, and proven strategies to prevent them in production. ## Optional - [All status codes](https://siteerror.com/codes): Complete listing of every HTTP status code covered on the site, grouped by category. - [Homepage](https://siteerror.com): Search, featured codes, popular comparisons, and FAQ. - [Sitemap](https://siteerror.com/sitemap.xml): Full XML sitemap of all pages.