HTTP status code messages for Web Developers and SEOs

Understanding HTTP Status Codes: A Comprehensive Guide for Web Developers and SEOs

Master the language of the web with this in-depth look at HTTP status codes and their critical role in website performance, user experience, and search engine optimization (SEO).

HTTP status code messages for Web Developers and SEOs

Every time your browser communicates with a web server, they exchange information using a set of rules called HTTP (Hypertext Transfer Protocol). A crucial part of this communication is the **HTTP status code**, a three-digit number returned by the server to indicate the status of the request. Understanding these codes is fundamental for web developers, system administrators, and especially for anyone involved in Search Engine Optimization (SEO).

From a successful page load to a missing resource or a server hiccup, HTTP status codes provide immediate insights into what happened. For SEO, knowing these codes is paramount. Incorrectly handled codes can lead to lost rankings, wasted crawl budget, and a poor user experience. Let's dive into the different categories of HTTP status codes.

✅ 1xx: Informational Responses

These codes indicate that the request has been received and understood. They are provisional responses, indicating that the server is continuing to process the request. They are rarely seen by end-users.

Code	Meaning
HTTP 100	Continue: The server has received the request headers and the client should proceed to send the request body.
HTTP 101	Switching Protocols: The server understands and is willing to comply with the client's request, via the Upgrade header field, to change the application protocol being used on this connection.
HTTP 102	Processing (WebDAV): An interim response used to inform the client that the server has accepted the complete request, but has not yet completed it.
HTTP 103	Early Hints: Primarily intended to allow user agents to start preloading resources while the server is still preparing the final response.

🟢 2xx: Success

These codes indicate that the client's request was successfully received, understood, and accepted. These are the most desirable codes for both users and search engines.

Code	Meaning
HTTP 200	OK: The standard response for successful HTTP requests. The requested resource has been successfully retrieved.
HTTP 201	Created: The request has been fulfilled and resulted in a new resource being created. Often used after a POST request.
HTTP 202	Accepted: The request has been accepted for processing, but the processing has not been completed.
HTTP 203	Non-Authoritative Information: The server is a transforming proxy that received a 200 OK from its origin, but is returning a modified version of the response.
HTTP 204	No Content: The server successfully processed the request, but is not returning any content. Useful for 'save' buttons on single-page applications.
HTTP 205	Reset Content: The server successfully processed the request, but requests that the client reset its document view.
HTTP 206	Partial Content: The server is delivering only part of the resource due to a range header sent by the client. Useful for large file downloads or video streaming.
HTTP 207	Multi-Status (WebDAV): A Multi-Status response conveys information about multiple resources in situations where multiple status codes might be appropriate.
HTTP 208	Already Reported (WebDAV): Used inside a DAV:propstat response element to avoid enumerating the internal members of multiple bindings to the same collection repeatedly.
HTTP 226	IM Used: The server has fulfilled a GET request for the resource, and the response is a representation of the result of one or more instance-manipulations applied to the current instance.

🟡 3xx: Redirection

These codes indicate that further action needs to be taken by the user agent to fulfill the request. This is critical for SEO, as proper redirection ensures link equity is passed and users reach the correct destination.

Code	Meaning
HTTP 300	Multiple Choices: Indicates multiple options for the resource from which the client may choose.
HTTP 301	Moved Permanently: The requested resource has been permanently moved to a new URI. This is the most SEO-friendly redirect, passing almost all link equity.
HTTP 302	Found: (Formerly "Moved Temporarily") The requested resource resides temporarily under a different URI. Use 302 for temporary redirects where the original URL might return later.
HTTP 303	See Other: The response to the request can be found under another URI using a GET method. Often used after a POST request to prevent re-submission issues.
HTTP 304	Not Modified: Indicates that the resource has not been modified since the version specified by the request headers. Saves bandwidth and speeds up page load.
HTTP 305	Use Proxy (deprecated): The requested resource must be accessed through the proxy given by the Location field. (Deprecated for security reasons).
HTTP 306	Switch Proxy (unused): No longer used, but reserved.
HTTP 307	Temporary Redirect: The requested resource resides temporarily under a different URI. The user agent must not change the request method if it performs an automatic redirection. Preserves the HTTP method.
HTTP 308	Permanent Redirect: The requested resource has been permanently moved to a new URI. Similar to 301, but specifically states that the request method should not be changed. Highly recommended for permanent redirects in modern web development.

🔴 4xx: Client Errors

These codes indicate that there was an error with the client's request. This could be due to incorrect syntax, missing authentication, or a resource that doesn't exist. These require immediate attention for SEO, as they can significantly impact crawlability and user experience.

Code	Meaning
HTTP 400	Bad Request: The server cannot or will not process the request due to an apparent client error (e.g., malformed request syntax).
HTTP 401	Unauthorized: The request requires user authentication. Often seen with protected pages.
HTTP 402	Payment Required (Reserved): Reserved for future use. Intended to be used for digital payment systems.
HTTP 403	Forbidden: The server understood the request but refuses to authorize it. Unlike 401, authentication will not help.
HTTP 404	Not Found: The server cannot find the requested resource. A very common error, often indicating broken links or removed pages. Implement custom 404 pages for better user experience.
HTTP 405	Method Not Allowed: The method specified in the request is not allowed for the resource identified by the request URI.
HTTP 406	Not Acceptable: The server cannot produce a response matching the list of acceptable values defined in the request's proactive negotiation headers.
HTTP 407	Proxy Authentication Required: The client must first authenticate itself with the proxy.
HTTP 408	Request Timeout: The server timed out waiting for the request.
HTTP 409	Conflict: Indicates that the request could not be processed because of a conflict in the current state of the resource.
HTTP 410	Gone: The requested resource is no longer available at the server and no forwarding address is known. Use 410 instead of 404 for permanently removed content to signal search engines to de-index faster.
HTTP 411	Length Required: The server refuses to accept the request without a defined Content-Length header.
HTTP 412	Precondition Failed: The server does not meet one of the preconditions that the requester put on the request header fields.
HTTP 413	Payload Too Large: The request entity is larger than the server is willing or able to process.
HTTP 414	URI Too Long: The URI provided was too long for the server to process.
HTTP 415	Unsupported Media Type: The request entity has a media type which the server or resource does not support.
HTTP 416	Range Not Satisfiable: The client has asked for a portion of the file (byte range), but the server cannot supply that portion.
HTTP 417	Expectation Failed: The expectation given in the request's Expect header field could not be met by at least one of the inbound servers.
HTTP 418	I'm a teapot (RFC 2324): This code was defined in 1998 as one of the traditional IETF April Fools' jokes. It's not intended to be implemented by HTTP servers.
HTTP 421	Misdirected Request: The request was directed at a server that is not able to produce a response.
HTTP 422	Unprocessable Entity (WebDAV): The server understands the content type of the request entity, but was unable to process the contained instructions.
HTTP 423	Locked (WebDAV): The resource that is being accessed is locked.
HTTP 424	Failed Dependency (WebDAV): The request failed because it depended on another request and that request failed.
HTTP 425	Too Early: Indicates that the server is unwilling to risk processing a request that might be replayed.
HTTP 426	Upgrade Required: The client should switch to a different protocol such as TLS/1.0, given in the Upgrade header field.
HTTP 428	Precondition Required: The origin server requires the request to be conditional.
HTTP 429	Too Many Requests: The user has sent too many requests in a given amount of time ("rate limiting").
HTTP 431	Request Header Fields Too Large: The server is unwilling to process the request because its header fields are too large.
HTTP 451	Unavailable For Legal Reasons: An operator has received a legal demand to deny access to a resource or to a set of resources that includes the requested resource.

🔵 5xx: Server Errors

These codes indicate that the server failed to fulfill an apparently valid request. These are serious issues that need immediate attention from the website's technical team, as they directly impact website availability and user trust.

Code	Meaning
HTTP 500	Internal Server Error: A generic error message, given when an unexpected condition was encountered and no more specific message is suitable. Requires investigation into server logs.
HTTP 501	Not Implemented: The server does not support the functionality required to fulfill the request.
HTTP 502	Bad Gateway: The server, while acting as a gateway or proxy, received an invalid response from an inbound server it accessed while attempting to fulfill the request.
HTTP 503	Service Unavailable: The server is currently unable to handle the request due to a temporary overload or scheduled maintenance, which will likely be alleviated after some delay. Crucial for SEO, as it tells search engines to come back later without losing rank.
HTTP 504	Gateway Timeout: The server, while acting as a gateway or proxy, did not receive a timely response from an upstream server.
HTTP 505	HTTP Version Not Supported: The server does not support the HTTP protocol version used in the request.
HTTP 506	Variant Also Negotiates: The server has an internal configuration error: the chosen variant resource is configured to engage in transparent content negotiation itself, and is therefore not a proper end point in the negotiation process.
HTTP 507	Insufficient Storage (WebDAV): The server is unable to store the representation needed to complete the request.
HTTP 508	Loop Detected (WebDAV): The server detected an infinite loop while processing the request.
HTTP 510	Not Extended: The policy for accessing the resource has not been met in the request's E.G. (Extended Guidance) header field.
HTTP 511	Network Authentication Required: The client needs to authenticate to gain network access.

HTTP Status Codes 400 to 416

Frequently Asked Questions (FAQs) about HTTP Status Codes

Q1: Why are HTTP status codes important for SEO?

A1: HTTP status codes are crucial for SEO because they tell search engine crawlers (like Googlebot) the exact status of a page. A 200 OK tells them the page is healthy and can be indexed. A 301 redirect correctly passes link equity to a new URL. A 404 or 500 signals a problem that can lead to de-indexing or a decline in rankings. Proper handling of these codes ensures efficient crawling, indexing, and prevents negative impacts on your site's visibility.

Q2: What is the difference between a 301 and a 302 redirect for SEO?

A2: A 301 Moved Permanently redirect tells search engines that a page has moved permanently to a new URL, transferring almost all of its link equity (ranking power) to the new location. This is ideal for permanent URL changes. A 302 Found (or Temporary Redirect) indicates a temporary move and generally passes less or no link equity. It should be used for short-term redirects, like A/B testing or site maintenance, when the original URL is expected to return.

Q3: How do 404 errors impact my website's SEO?

A3: While an occasional 404 isn't catastrophic, a large number of 404 errors can negatively impact SEO. They signal to search engines that your site might be poorly maintained, leading to wasted crawl budget (Googlebot spends time on non-existent pages instead of valuable ones). More importantly, 404s create a poor user experience, as visitors land on broken pages, which can increase bounce rates and harm your site's reputation. It's best to fix 404s by redirecting to relevant new pages or restoring content.

Q4: What should I do if my website is returning 5xx server errors?

A4: 5xx server errors (like 500 Internal Server Error, 502 Bad Gateway, 503 Service Unavailable) are critical and indicate a problem on your web server. These errors severely impact user experience and can lead to immediate de-indexing by search engines if prolonged. You should immediately investigate server logs, check server resources, review recent code deployments, and contact your hosting provider if necessary. For temporary issues like maintenance, a 503 Service Unavailable with a "Retry-After" header is the most SEO-friendly response.

Q5: Can HTTP status codes affect my site's crawl budget?

A5: Yes, absolutely. Your crawl budget is the number of pages search engine bots will crawl on your site within a given timeframe. Frequent 4xx and 5xx errors waste crawl budget, as bots spend time trying to access problematic pages instead of discovering and indexing new or updated valuable content. Proper use of 301 redirects and addressing errors efficiently helps preserve and optimize your crawl budget.