If you’ve ever encountered a “404 Not Found” or a “500 Internal Server Error” while browsing, you’ve already met HTTP response status codes. These three-digit numbers are part of every interaction between your browser and a website server. While they might seem cryptic at first, understanding them can unlock deep insights into site performance, SEO health, and user experience.
This guide walks you through all HTTP response codes, what they mean, and why staying on top of them is essential for web developers, digital marketers, SEOs, and business owners alike.
What Are HTTP Response Status Codes?
HTTP response status codes are standardized numbers that indicate the result of a client’s request to a server. Every time you visit a webpage, your browser sends a request—and the server responds with the requested content and an HTTP status code. This code tells the browser what happened: whether it was successful, redirected, failed, or not authorized.
- Think of HTTP request response codes as digital traffic signals:
Green (2xx): All clear. - Yellow (3xx): Proceed with detours.
- Red (4xx/5xx): Error—stop or fix required.
Why Understanding HTTP Status Codes Matters
Whether you’re a developer fixing bugs or an SEO optimizing crawlability, HTTP code responses are central to managing and improving a website.
- Developers: Diagnose bugs and server misconfigurations faster.
- SEOs: Detect crawl errors, redirect loops, and indexing issues.
- Business owners: Ensure that users have a smooth, uninterrupted experience, leading to better conversions and engagement.
Misusing or neglecting HTTP response status codes can harm rankings, confuse users, and degrade trust in your website.
Complete List of All HTTP Response Codes
Let’s break down all HTTP response codes by category:
1xx – Informational (The request is being processed)
- 100: Continue – The server has received the request headers and the client can proceed with the body.
- 101: Switching Protocols – The server agrees to switch protocols as requested by the client.
- 102: Processing (WebDAV) – The server is processing the request but hasn’t completed it yet.
- 103: Early Hints – Preliminary headers are sent before the final response, typically used to preload assets.
These are mostly invisible to users but crucial for low-level protocol operations.
2xx – Success (The request was successful)
- 200: OK – The request was successful and the server returned the requested data.
- 201: Created – The request was successful and a new resource was created.
- 202: Accepted – The request has been accepted but not yet processed.
- 203: Non-Authoritative Information – The response is from a third-party source, not the original server.
- 204: No Content – The request was successful but there’s no content to return.
- 205: Reset Content – The client should reset the document view (e.g., a form) after the request.
- 206: Partial Content – The server is returning only part of the requested resource (used for range requests).
- 207: Multi-Status (WebDAV) – The response includes multiple status codes for different operations in a single request.
- 208: Already Reported – The resource has already been reported earlier in this request (WebDAV).
- 226: IM Used – The server fulfilled the request using an instance-manipulation (e.g., delta encoding).
When your site works as intended, a 200 HTTP status code is silently doing its job.
3xx – Redirection (Further action is needed)
- 300: Multiple Choices – The requested resource has multiple representations to choose from.
- 301: Moved Permanently – The resource has permanently moved to a new URL (SEO-critical redirect).
- 302: Found – The resource is temporarily located at a different URL.
- 303: See Other – The response should be retrieved using a GET request at a different URL.
- 304: Not Modified – The cached version of the resource is still valid.
- 305: Use Proxy (Deprecated) – The resource must be accessed through a proxy (now deprecated).
- 306: (Unused) – Reserved for future use; currently not in use.
- 307: Temporary Redirect – Temporarily redirects while preserving the HTTP method.
- 308: Permanent Redirect – Permanently redirects while preserving the HTTP method.
Redirection HTTP request response codes are vital for managing link equity and smooth transitions.
4xx – Client Errors (Problem with the request)
- 400: Bad Request – The server couldn’t understand the request due to malformed syntax.
- 401: Unauthorized – Authentication is required to access the resource.
- 402: Payment Required (Reserved) – Reserved for future use, originally intended for digital payments.
- 403: Forbidden – Access is denied, even if you’re authenticated.
- 404: Not Found – The requested resource could not be found on the server.
- 405: Method Not Allowed – The requested method is not supported for the targeted resource.
- 406: Not Acceptable – The server cannot return content matching the client’s Accept headers.
- 407: Proxy Authentication Required – Authentication with a proxy server is needed.
- 408: Request Timeout – The client took too long to send the request.
- 409: Conflict – The request could not be completed due to a conflict with current server state.
- 410: Gone – The resource is no longer available and will not be restored.
- 411: Length Required – The server requires a Content-Length header to process the request.
- 412: Precondition Failed – One or more conditions given in the request headers were not met.
- 413: Payload Too Large – The request body is larger than the server is willing to process.
- 414: URL Too Long – The requested URI is longer than the server can handle.
- 415: Unsupported Media Type – The server does not support the media type of the request payload.
- 416: Range Not Satisfiable – The requested byte range cannot be fulfilled.
- 417: Expectation Failed – The server could not meet the requirements of the Expect header.
- 418: I’m a Teapot – A humorous code from an April Fools’ RFC; not meant for real-world use.
- 421: Misdirected Request – The request was sent to a server that can’t produce a valid response.
- 422: Unprocessable Entity – The server understands the request but cannot process it (often semantic errors).
- 423: Locked – The resource is locked and cannot be accessed or modified.
- 424: Failed Dependency – A previous request failed, causing this dependent request to fail.
- 425: Too Early – The server is unwilling to process the request as it might be replayed.
- 426: Upgrade Required – The client should switch to a different protocol, such as TLS/1.3.
- 428: Precondition Required – The origin server requires the request to be conditional.
- 429: Too Many Requests – The user has sent too many requests in a given amount of time (rate limit).
- 431: Request Header Fields Too Large – The headers are too large for the server to process.
- 451: Unavailable for Legal Reasons – The resource is blocked due to legal demands (e.g., censorship, court orders).
A high volume of 4xx HTTP response status codes often means broken links or accessibility issues that should be fixed immediately.
5xx – Server Errors (Problem with the server)
- 500: Internal Server Error – A generic server error occurred and the server doesn’t have a more specific explanation.
- 501: Not Implemented – The server doesn’t support the functionality required to fulfill the request.
- 502: Bad Gateway – The server received an invalid response from an upstream server.
- 503: Service Unavailable – The server is currently overloaded or down for maintenance.
- 504: Gateway Timeout – The server didn’t get a timely response from an upstream server.
- 505: HTTP Version Not Supported – The server doesn’t support the HTTP protocol version used in the request.
- 506: Variant Also Negotiates – Server misconfiguration; content negotiation resulted in a loop.
- 507: Insufficient Storage – The server is out of space and can’t store the representation needed to complete the request.
- 508: Loop Detected – A server-side loop was found during request processing.
- 510: Not Extended – Further extensions to the request are required for the server to process it.
- 511: Network Authentication Required – The client needs to authenticate to gain network access (commonly seen in captive portals).
All HTTP response codes in the 5xx range indicate server-side problems. If persistent, they affect search engine crawling and user trust.
How to Monitor and Fix HTTP Status Codes
Recommended Tools:
- Google Search Console – Monitors crawl issues and HTTP status codes.
- Screaming Frog SEO Spider – Crawls all site URLs to extract http code responses.
- Server Logs – Offer real-time access to http request response codes for every interaction.
Common Fixes:
- Set up 301 redirects for broken pages.
- Resolve server configuration issues causing 500 series errors.
- Avoid chains like 301 → 302 → 200 which dilute SEO value.
- Clean up sitemap and robots.txt to avoid pointing to 404 pages.
Final Thoughts
Mastering HTTP response status codes is essential—not just for web developers, but for anyone serious about managing a digital presence. Every HTTP code response provides insight into the health and behavior of your website.
From fixing crawl issues to improving user journeys, understanding HTTP status codes allows you to proactively maintain performance, protect SEO, and ensure a smooth user experience.
Need help interpreting or repairing your site’s HTTP request response codes? Browse our Website Performance Services or explore more tutorials in our Blog Section to take control of your site’s backend health today.
