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A Deep Dive into HTTP Status Codes and Their Significance

Apr 12 2024 by Oskay Günaçar

What Are HTTP Status Codes?

HTTP status codes are standardized responses issued by a server in response to a client's request on the internet. These codes are part of the HTTP (Hypertext Transfer Protocol), which is the foundation of data communication on the World Wide Web. Each status code provides information about the result of the request. They are grouped into five classes, each defined by the first digit, indicating the type of response:

1xx: Informational

These codes indicate a provisional response, specifying that the request has been received and the process is continuing. For example, 100 Continue tells the client that the initial part of the request has been received and the client should continue with its request.

2xx: Success

This class of status codes indicates that the client's request was successfully received, understood, and accepted. 200 OK is the most common success code, indicating that the request has succeeded.

3xx: Redirection

These codes tell the client that further action needs to be taken in order to complete the request. This usually involves the client making a new request to a different URL. For instance, 301 Moved Permanently is used to redirect to a new URL permanently, while 302 Found indicates a temporary redirection.

4xx: Client Error

These codes are used when there was an error and the request could not be completed as intended. It usually indicates an issue on the client's side. For example, 404 Not Found indicates that the requested resource could not be found on the server.

5xx: Server Error

This class of codes indicates that the server failed to fulfill a valid request, suggesting a problem on the server's side. 500 Internal Server Error is a generic error message when the server encounters an unexpected condition that prevents it from fulfilling the request.

HTTP status codes are essential for diagnosing and resolving issues with websites and applications, helping developers understand the state of the request-response cycle, and guiding them in troubleshooting problems.

Detailed Overview of HTTP Status Codes

1xx: Informational Responses

The 1xx series signifies preliminary responses that inform the client that the request has been received and understood, and processing is continuing. It is crucial in optimizing client-server interactions by facilitating the handling of complex operations or large data transfers.

  • 100 Continue: Encourages the client to proceed with its request, typically after sending a preliminary header indicating the size of the request body.
  • 101 Switching Protocols: Acknowledges the client’s request to change the communication protocol.
  • 102 Processing (WebDAV): Indicates that the server has received and is processing the request but no response is available yet.
  • 103 Early Hints: Provides preliminary headers before the server has prepared the full response, allowing the client to start preloading resources.

2xx: Successful Responses

The 2xx status codes confirm that the client's request was successfully received, understood, and accepted. These codes are indicative of a successful interaction and are what developers aim to receive for most requests.

  • 200 OK: The request has succeeded, and the response contains the requested data.
  • 201 Created: A new resource has been created as a result of the request.
  • 202 Accepted: The request has been accepted for processing, but the processing is not complete.
  • 203 Non-Authoritative Information: The returned metadata is not exactly the same as available from the origin server but collected from a local or third-party copy.
  • 204 No Content: The server successfully processed the request, but is not returning any content.
  • 205 Reset Content: Directs the client to reset the document view, such as clearing form data or refreshing a page.
  • 206 Partial Content: Indicates that the server is delivering only part of the resource due to a range header sent by the client.

3xx: Redirection Messages

Redirection codes, denoted by 3xx, signal that further action needs to be taken by the client to fulfill the request. These are pivotal for resource relocation, load balancing, and conditional requests.

  • 300 Multiple Choices: Indicates multiple options for the resource that the client may follow.
  • 301 Moved Permanently: The URL of the requested resource has been changed permanently.
  • 302 Found: The server has found a temporary redirection. This response is used for redirecting without changing the request method.
  • 303 See Other: The response to the request can be found under another URI using the GET method.
  • 304 Not Modified: Indicates that the resource has not been modified since the last request.
  • 307 Temporary Redirect: The request should be repeated with another URI, but future requests should still use the original URI.
  • 308 Permanent Redirect: The request and all future requests should be repeated using another URI.

4xx: Client Error Responses

These statuses indicate an error resulting from the client's request, suggesting incorrect syntax, infeasibility of fulfillment, or authentication issues.

  • 400 Bad Request: The server cannot process the request due to a client error.
  • 401 Unauthorized: Authentication is required and has failed or has not yet been provided.
  • 403 Forbidden: The server understood the request but refuses to authorize it.
  • 404 Not Found: The requested resource could not be found but may be available in the future.
  • 405 Method Not Allowed: The request method is known by the server but has been disabled and cannot be used.
  • 406 Not Acceptable: The server cannot produce a response matching the list of acceptable values defined in the request's proactive content negotiation headers.
  • 407 Proxy Authentication Required: Similar to 401, but it indicates that the client must first authenticate itself with the proxy.
  • 408 Request Timeout: The server timed out waiting for the request.
  • 409 Conflict: The request could not be processed because of conflict in the request, such as an edit conflict.
  • 410 Gone: The requested resource is no longer available and will not be available again.

5xx: Server Error Responses

The 5xx series of status codes indicate that the server has encountered an error or is incapable of performing the request. These errors suggest issues on the server side that prevent the execution of the request.

  • 500 Internal Server Error: A generic error message when the server encounters an unexpected condition.
  • 501 Not Implemented: The server either does not recognize the request method, or it lacks the ability to fulfill the request.
  • 502 Bad Gateway: The server, while acting as a gateway or proxy, received an invalid response from the upstream server.
  • 503 Service Unavailable: The server cannot handle the request (because it is overloaded or down for maintenance).
  • 504 Gateway Timeout: The server, while acting as a gateway or proxy, did not receive a timely response from the upstream server.
  • 505 HTTP Version Not Supported: The server does not support the HTTP protocol version used in the request.
  • 506 Variant Also Negotiates (Experimental): A server configuration error that causes circular reference in the variant negotiation process.
  • 507 Insufficient Storage (WebDAV): The server is unable to store the representation needed to complete the request.
  • 508 Loop Detected (WebDAV): The server detected an infinite loop while processing the request.
  • 510 Not Extended: Further extensions to the request are required for the server to fulfill it.
  • 511 Network Authentication Required: Indicates that the client needs to authenticate to gain network access.

Utilizing HTTP Status Codes Effectively

The correct usage of HTTP status codes is essential for developing efficient web applications and for troubleshooting and resolving issues in web communication. By employing the most appropriate status codes, developers and administrators can provide clear, precise feedback to clients, aiding in the quick resolution of errors and optimizing the user experience. To this end, it is recommended to:

  • Adopt specific codes for precise scenarios: Utilizing the most specific HTTP status code available for a given situation can greatly aid in diagnosing and understanding web communication issues.
  • Design user-friendly error messages: Especially for 4xx and 5xx status codes, providing clear and helpful error messages can improve the user experience during error conditions.
  • Monitor and log status codes: Keeping track of the frequency and types of status codes returned by a server can help identify trends, potential issues, and opportunities for optimization in web services.

Why HTTP Status Codes Are Important for SEO?

Search engine bots, especially Google bots, come to your website for certain periods of time and crawl your site. During these crawls, HTTP responses sent from the server for your pages are also processed by search engine bots. In this context, when search engine bots, especially Google bots, send a request related to any page of your site, it makes sense of the response from the server and includes it in the algorithmic processes by marking whether your page is working or not, or if it is working, the way it works.

In SEO studies and indexing processes in search engines, HTTP 100 and 200 coded responses are not a problem, they are even indicators that the site is working properly and do not negatively affect search engine processes. However, HTTP responses with 4xx (400) and 5xx (500) codes convey to search engine bots that there are certain problems on the user or server side, and this affects the evaluation processes of your pages depending on the cause of the relevant situation.

HTTP responses with error codes 4xx and especially 5xx negatively consume your site's crawl budget and in many cases can affect your site's crawl indexing processes by sending negative signals to search engine bots about your site's crawlability.

Websites with a large number of 4xx and 5xx error-coded URLs may have their crawl budgets (crawl frequency) reduced by search engines if they do not correct the relevant errors, and the related situation (depending on the error) may affect the overall quality signals of the site and cause ranking losses.
Finally, 3xx (300) HTTP codes are the class that refers to redirected links as mentioned in the section above. Since a redirection process is applied on pages with 3xx HTTP status codes, the browser is informed about the relevant status. This situation, which is not visible in the browser by the user, has an extremely important effect such as pagerank transfer on the SEO side.

301 (permanent redirect) A page redirected by permanent redirect can transfer its current pagerank activity to the page to which it is redirected without any loss. The most basic criterion for achieving this is to inform search engines through HTTP status codes that a page has been permanently redirected to another page.

In 302 and 307 redirects, which are not 301 HTTP status codes, there is no pagerank transfer because the redirect is for "temporary" or "security" purposes.

What Are The Most Important Status Codes For SEO?

1. 200 OK

This status code indicates that the request was successful, and the browser was able to retrieve the requested page. It's the ideal status for any URL as it means content is accessible and can be indexed by search engines.

2. 301 Moved Permanently

This is used for permanent URL redirection. It's crucial for SEO when you move or rename a page and want to ensure that the link equity (ranking power) is passed to the new URL.

3. 302 Found (Moved Temporarily)

Similar to 301 but for temporary redirection. Search engines may treat frequent or long-standing 302s like 301s, so it's important to use them correctly to avoid diluting link equity.

4. 404 Not Found

This indicates that the server can't find the requested resource. While sometimes unavoidable, too many 404 errors can harm your site's usability and rankings. Regularly monitoring and fixing broken links is essential.

5. 410 Gone

This status code is similar to 404 but indicates that the resource was deliberately removed and will not be coming back. It's a stronger signal to search engines to de-index the page.

6. 500 Internal Server Error

This indicates a generic error message when the server encounters an unexpected condition that prevents it from fulfilling the request. Frequent 500 errors can negatively impact your site's rankings as they degrade the user experience.

7. 503 Service Unavailable

This code means the server is not ready to handle the request, often due to maintenance or overloading. Using this status code correctly during planned downtime can prevent search engines from assuming a page has permanently gone, protecting your rankings.

Each of these status codes plays a significant role in website management and SEO. They help ensure that users and search engines are directed to the correct content, improving site performance and visibility in search results. Regularly auditing your site's status codes can identify and resolve issues that might otherwise hinder your SEO efforts.

Conclusion

HTTP status codes are a fundamental aspect of the protocol that powers the web, offering a standardized means for servers to communicate the outcome of a client's request. A comprehensive understanding of these codes, their meanings, and their appropriate usage is indispensable for web developers, network administrators, and IT professionals aiming to ensure smooth, efficient, and effective web communications. By adhering to the standards and best practices associated with HTTP status codes, professionals can enhance the reliability, usability, and performance of web applications and services, ultimately contributing to a more robust and user-friendly internet ecosystem.

Oskay Günaçar
Oskay Günaçar is a Technical SEO expert and backend developer. His main areas of interest are back-end programming, Python, Django, Go, semantic SEO, technical SEO. With more than 5 years of SEO experience, he has held SEO specialist positions at İkiler, Webtures, Boosmart, and Storyly.io companies, and has been involved in numerous projects as an outsourced expert. Through the TechSEOHub website, he aims to share the expertise and experience he has gained from managing and developing (SEO) processes for many successful and large websites in the industry, and to produce content for easy access to accurate and high-quality information.