# 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 403 Forbidden: Authorization, the 401 vs 403 Trap, and When to Hide a Resource Entirely](https://siteerror.com/blog/understanding-403-forbidden): What 403 Forbidden really means (authorization, not authentication), why logging in won't fix it, how it differs from 401, 404, and 407, and how to return and handle it correctly across Express, Next.js, NGINX, and Apache.
- [Understanding HTTP 308 Permanent Redirect: Method-Preserving Redirects Done Right](https://siteerror.com/blog/understanding-308-permanent-redirect): How 308 Permanent Redirect differs from 301, why it preserves the HTTP method, the full 301/302/303/307/308 matrix, framework gotchas (including Next.js), caching, and SEO.
- [Understanding HTTP 401 Unauthorized: Authentication, WWW-Authenticate, and the 401 vs 403 Trap](https://siteerror.com/blog/understanding-401-unauthorized): What 401 Unauthorized really means (authentication, not authorization), why the WWW-Authenticate header is mandatory, when to use 401 vs 403 vs 407, and how to return and handle it correctly.
- [Understanding HTTP 404 Not Found: Why It Happens and What to Do About It](https://siteerror.com/blog/understanding-404-not-found): The internet's most famous error explained — what 404 really means, when to use it vs. 410 or 403, how it affects SEO, and how to build a 404 page that doesn't lose users.
- [Understanding HTTP 503 Service Unavailable: Planned Downtime, Overload, and Graceful Failure](https://siteerror.com/blog/understanding-503-service-unavailable): A deep dive into HTTP 503 — when to return it, why Retry-After matters, how to ship maintenance windows without trashing your SEO, and the differences between 503, 500, 502, and 429.
- [Understanding HTTP 103 Early Hints: Faster Pages with Smarter Preloads](https://siteerror.com/blog/understanding-103-early-hints): How HTTP 103 Early Hints lets the server tell the browser what to preload before the real response is ready — what it does, when it helps, and how to ship it.
- [Understanding NGINX 499 Client Closed Request: When Your Users Give Up First](https://siteerror.com/blog/understanding-499-client-closed-request): A deep dive into NGINX's 499 status code — what it means when the client hangs up before the server can respond, and how to use it as a leading indicator of problems.
- [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.