HTTP Status Codes: Full List of 40+ Explained & How to Fix Errors

Updated by Chima Mmeje — March 24, 2025.

An HTTP status code is a three-digit number sent by a web server in response to a request from a client, such as a browser or a search engine crawler like Googlebot. These codes are part of the Hypertext Transfer Protocol (HTTP) and indicate whether a request was successful, redirected, or resulted in an error.

Whenever you visit a website, your browser sends an HTTP request to the server hosting the site. The server processes the request and responds with a status code, which helps determine the next steps. For example, a 200 OK status means the page loaded correctly, while a 404 not found means the requested resource does not exist.

Status codes play a critical role in SEO, web development, and server management. Search engines like Google and Bing use them to determine if a webpage should be indexed, while tools like Google Search Console, cURL, and browser DevTools help developers diagnose website issues.

Each HTTP status code follows a standardized three-digit format defined by the Internet Assigned Numbers Authority (IANA) and documented in the RFC 9110 specification maintained by the Internet Engineering Task Force (IETF).

HTTP status codes are grouped into five categories based on their first digit. Each category represents a general type of server response, helping users and search engines understand how a request was handled.

• 1xx – informational: The request has been received, and the server is continuing to process it. 
• 2xx – success: The request was successfully completed, and the response contains the requested resource. 
• 3xx – redirection: The client must take additional action to complete the request, often involving a URL change.
• 4xx – client error: The request cannot be fulfilled due to an issue on the client side, such as a missing page or incorrect permissions.
• 5xx – server error: The server failed to process a valid request due to an internal issue. Example: 

Understanding these categories helps website owners, developers, and digital marketers diagnose and fix problems that affect page speed, SEO rankings, and user experience.

HTTP status codes provide essential information about how a request was processed. Below is a breakdown of all major codes, their meanings, and troubleshooting tips where applicable.

1xx – informational responses

These codes indicate that the server has received the request and is processing it but has not yet provided a final response.

• 100 continue: The server has received the request headers and expects the client to continue sending the request body.
• 101 switching protocols: The server is switching to a different communication protocol as requested by the client.
• 103 early hints: Used to preload resources before the final response is sent, improving page load performance.

Common use cases include chunked transfers (100 continue) and preloading resources (103 early hints) to improve performance.

2xx – success responses

These codes confirm that a request was successfully received, understood, and processed.

• 200 OK: The request was successful, and the server has returned the requested resource.
• 201 created: A new resource was successfully created, often used in API responses.
• 204 no content: The request was successful, but there is no additional content to return.

Common use cases include webpage loads (200 OK), API responses (201 created), and tracking scripts (204 no content).

3xx – redirection responses

Redirection codes inform the client that further action is required to complete the request.

• 301 moved permanently: The resource has been permanently redirected to a new URL. Search engines will transfer ranking signals to the new location.
• 302 found: The resource is temporarily available at a different URL but may change later.
• 303 see other: The response to the request can be found under a different URI and should be retrieved using a GET method on that resource. This status code is typically used to redirect after a POST request.
• 304 not modified: The requested resource has not changed since the last access, allowing the browser to load it from cache.
• 305 use proxy: The requested resource must be accessed through the proxy given by the Location field. This status code is not widely used due to security concerns.
• 306 (unused): This status code was used in a previous version of the specification but is no longer used and is reserved for future use.
• 307 temporary redirect: The requested resource resides temporarily under a different URI. The method and the body of the original request are reused to perform the redirected request.
• 308 permanent redirect: This status code indicates that the requested resource has been permanently assigned a new URI, and any future references should use the new URI. Unlike 301, the method and the body of the original request are reused to perform the redirected request.

Common use cases include URL changes (301), temporary A/B testing (302), and browser caching (304).

4xx – client errors

These errors indicate that the request was invalid or cannot be fulfilled by the server due to an issue on the client’s side.

• 400 bad request: The server cannot process the request due to malformed syntax or missing parameters.
• 401 unauthorized: Authentication is required, but the credentials provided are missing or incorrect.
• 402 payment required: This status code is reserved for future use and is not currently implemented.
• 403 forbidden: The server understands the request but refuses to authorize it.
• 404 not found: The requested resource is not available on the server.
• 405 method not allowed: The method specified in the Request-Line is not allowed for the resource identified by the Request-URI. For example, a POST request on a read-only resource.
• 406 not acceptable: The requested resource is only capable of generating response entities that have content characteristics not acceptable according to the accept headers sent in the request.
• 407 proxy authentication required: This status code is similar to 401 (Unauthorized), but it indicates that the client must first authenticate itself with the proxy.
• 408 request timeout: The client did not produce a request within the time that the server was prepared to wait. The client may repeat the request without modifications at any later time.
• 409 conflict: The request could not be completed due to a conflict with the current state of the resource. This code is used in situations where the user might be able to resolve the conflict and resubmit the request.
• 410 gone: The requested resource is no longer available at the server and no forwarding address is known. This condition is expected to be considered permanent.
• 411 length required: The server refuses to accept the request without a defined Content-Length. The client may repeat the request if it adds a valid Content-Length header field.
• 412 precondition failed: The precondition given in one or more of the request-header fields evaluated to false when it was tested on the server.
• 413 request entity too large: The server is refusing to process a request because the request entity is larger than the server is willing or able to process.
• 414 request-URI too long: The server is refusing to service the request because the Request-URI is longer than the server is willing to interpret.
• 415 unsupported media type: The server is refusing to service the request because the entity of the request is in a format not supported by the requested resource for the requested method.
• 416 requested range not satisfiable: The server should return this status code if a request included a Range request-header field, and none of the range-specifier values in this field overlap the current extent of the selected resource.
• 417 expectation failed: The expectation given in an Expect request-header field could not be met by this server, or, if the server is a proxy, the server has unambiguous evidence that the request could not be met by the next-hop server.

Common use cases include API request failures (400), restricted content access (401, 403), and missing pages (404).

5xx – server errors

Server-side errors indicate that the server encountered a problem while trying to process a valid request.

• 500 internal server error: A generic error message indicating that something went wrong on the server.
• 501 not implemented: The server does not support the functionality required to fulfill the request. This status code indicates that the server does not recognize the request method or lacks the ability to fulfill the request.
• 502 bad gateway: The server acting as a gateway received an invalid response from an upstream server.
• 503 service unavailable: The server is temporarily unable to handle the request, often due to maintenance or high traffic.
• 504 gateway timeout: A server acting as a gateway did not receive a response from another server in time.
• 505 HTTP version not supported: The server does not support, or refuses to support, the HTTP protocol version that was used in the request message.
• 506 variant also negotiates: The server has an internal configuration error: the chosen variant resource is configured to engage in transparent negotiation itself, making it an improper endpoint in the negotiation process.
• 507 insufficient storage: The method could not be performed on the resource because the server is unable to store the representation needed to complete the request successfully.
• 508 loop detected: The server has detected an infinite loop while processing the request. This status code indicates that the server terminated an operation because it encountered an infinite loop.
• 510 not extended: Further extensions are required for the server to be able to fulfill the request. This status code indicates that the request cannot be processed until additional extensions are provided.
• 511 network authentication required: The client needs to authenticate to gain network access. This status code indicates that the client must authenticate itself to gain access to the network.

Common use cases include server crashes (500), gateway failures (502, 504), high-traffic downtime (503), and network login requirements (511).

Search engines like Google, Bing, and Yahoo rely on HTTP status codes to understand how a website’s content is structured and whether pages are accessible. These codes influence how pages are crawled, indexed, and ranked in search results. When used correctly, they help improve user experience and site performance.

SEO impact of HTTP status codes

1xx informational: Minimal SEO impact, but 103 early hints can improve Core Web Vitals by preloading resources faster.

2xx success: 200 OK ensures indexing, while 204 no content prevents unnecessary indexing of tracking requests.

3xx redirection: 301 redirects preserve rankings, 302 redirects may delay indexing updates, and 304 not modified helps with crawl efficiency by reducing redundant requests.

4xx client errors: 404 not found wastes crawl budget, while 403 forbidden can block important pages from being indexed.

5xx server errors: 500 internal server errors and 503 services unavailable can lead to deindexing if they persist, as search engines may consider the site unreliable.

How Google handles redirects (301 vs. 302)

Redirects tell search engines that a page has moved, but the type of redirect determines how rankings and link equity are affected.

• 301 moved permanently: Use when permanently moving a page, merging content, or updating URLs to ensure rankings and backlinks transfer. Google treats this as a strong signal to transfer ranking value to the new URL.
• 302 found (temporary redirect): Use for temporary changes, such as A/B testing or seasonal promotions, where the original URL will be restored. Google will continue to index the original URL rather than passing ranking signals to the redirected page.

Monitoring HTTP status codes is essential for maintaining a healthy website. A few best practices to follow include:

• Regularly audit redirects to avoid redirect chains and loops.
• Monitor Google Search Console for crawl errors and fix them promptly.
• Optimize server response times to prevent 5xx errors that can impact rankings.
• Use 301 redirects for permanent URL changes to retain search equity.
• Ensure 404 errors are properly handled to minimize crawl budget waste

HTTP status code errors like 4xx and 5xx can block users and search engines from reaching your content. These issues hurt crawlability, user experience, and rankings. 

You can quickly detect and resolve them with Moz Pro Site Crawl.

Step 1: Run an On-Demand Crawl

In Moz Pro, go to On-Demand Crawl from the left-hand menu. Enter the subdomain you want to audit and launch a crawl. Once complete, you’ll get a detailed crawl report highlighting technical SEO issues across your pages.

Step 2: Locate status code errors in the All Issues chart

At the top of your crawl report, scroll to the All Issues bar chart. Status code errors are grouped under Critical and shown in red. 

Look for:

• 4xx errors (like “404 Not Found”)
• 5xx errors (server errors)
• Redirect to 4xx

These highlight broken links, server issues, or redirect loops that need attention.

Step 3: Filter pages by status code

Scroll down to the Pages Crawled section. Open the Status Codes dropdown and check:

• 3xx to review redirects
• 4xx to see broken links
• 5xx to find server-side failures

This gives you a list of affected URLs, including the status code, number of issues, and crawl depth.

Step 4: Prioritize and fix issues

• 4xx errors usually mean the page doesn’t exist or the link is broken. Redirect to a live page or update internal links.
• 5xx errors signal server problems—work with your dev team to resolve these.
• Redirect to 4xx should be updated to point to valid, functioning URLs.

Fix these issues in your CMS, server settings, or via redirects.

Step 5: Rerun the crawl to confirm

After making fixes, run a new crawl to verify that the status code issues are resolved. This helps ensure your site is fully accessible to both users and search engines.

HTTP errors can negatively impact SEO, user experience, and website performance if not properly addressed. Below are common issues and step-by-step solutions for resolving them.

Fixing 404 not found errors

A 404 not found error occurs when a requested page does not exist on the server. While some 404s are inevitable, excessive errors can harm SEO by wasting crawl budget and frustrating users.

Step-by-step fixes:

Check for broken links: Use tools like Google Search Console, or Moz Site Crawl to identify internal and external links pointing to non-existent pages.

Set up 301 redirects: If a page has been moved or removed, redirect users to the most relevant existing page.

Customize your 404 page: Provide helpful links and a search bar to guide visitors to relevant content instead of leaving the site.

Monitor for recurring issues: Regularly audit your site to ensure old URLs are properly redirected.

Handling 500 internal server errors

A 500 internal server error indicates that something has gone wrong on the server, preventing it from completing the request. These errors can be caused by misconfigurations, corrupted files, or server overloads.

Step-by-step fixes:

Check server logs: Review Apache, Nginx, or IIS logs to identify the exact cause of the issue.

Increase PHP memory limits: If you are running a CMS like WordPress, increasing the memory allocation in the php.ini file may resolve the problem.

Inspect .htaccess and configuration files: Incorrect rules in .htaccess or server configuration files can lead to errors.

Check for plugin or theme conflicts: On platforms like WordPress, disable plugins and themes one by one to find the source of the issue.

Restart the server: If none of the above solutions work, restarting the web server or contacting your hosting provider may be necessary.

Regularly checking HTTP status codes helps maintain website health, improve SEO, and prevent user experience issues. Fixing 404 errors, 500 server issues, and incorrect redirects ensures smooth crawling and indexing. Use tools like Moz Site Crawl, Google Search Console, and Screaming Frog to identify problems early. 

What are error codes 200, 400, and 500?

A 200 OK status means the request was successful and the server returned the requested resource. A 400 bad request occurs when the server cannot process the request due to missing or incorrect information. A 500 internal server error indicates a problem on the server’s end, preventing it from completing the request.

What is the difference between HTTP 403 and 401?

Both errors relate to access restrictions, but they serve different purposes. A 401 unauthorized error means authentication is required but either missing or invalid, prompting the client to try again with proper credentials. A 403 forbidden error, on the other hand, means authentication was successful, but the user still does not have permission to access the resource.

What is the difference between 301 and 302 redirects?

A 301 moved permanently redirect tells search engines that the move is permanent, passing ranking value to the new URL. A 302 found redirect is temporary, meaning search engines will continue to index the original URL rather than transferring authority to the new destination.

What is the rarest HTTP status code?

Some HTTP status codes are rarely seen but still exist. For example, 418 I’m a teapot, originally created as an April Fools joke, remains a fun yet valid status code. 451 unavailable for legal reasons appears when content is blocked due to legal restrictions, such as government censorship or copyright claims. Another uncommon code is a 509 bandwidth limit exceeded, which occurs when a website surpasses its hosting provider’s allocated bandwidth.

Keep Learning

• Redirection
• Canonicalization
• The Beginner's Guide to SEO
• Are 404 Pages Always Bad for SEO?
• How Should You Handle Expired Content?

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