The Exhaustive Guide to HTTP Status Codes (2024 Edition)

If you‘ve spent any time on the web, you‘ve undoubtedly encountered an HTTP status code. Whether it‘s the dreaded 404 "Page Not Found" or the puzzling 500 "Internal Server Error," these codes are the web server‘s way of communicating the result of a request back to the client.

But far from being mere error messages, HTTP status codes are a critical component of the web‘s infrastructure. They provide a standardized way for web servers and clients to exchange metadata about each request and response.

As a web developer or site owner, having a solid understanding of HTTP status codes is essential. By monitoring and correctly utilizing status codes, you can:

  • Ensure your site is accessible and functioning properly
  • Provide a good user experience by handling errors gracefully
  • Debug and troubleshoot issues with your application or server
  • Maintain your site‘s search engine visibility and ranking

In this guide, we‘ll provide an exhaustive overview of HTTP status codes. We‘ll cover what they are, how they‘re structured, and most importantly, what each code really means. We‘ll also share best practices and tips for how to deal with common status codes on your site.

Whether you‘re building your first web app, optimizing your site‘s performance and SEO, or just curious about what‘s going on behind the scenes, this guide is for you. Let‘s get started!

HTTP Status Code 101

First, let‘s define exactly what we‘re talking about. An HTTP status code is a 3-digit number that the server sends in its response header to indicate the result of the client‘s HTTP request. The status code is accompanied by a short description phrase, like "OK" or "Not Found."

For example, here‘s what a successful response header might look like:

HTTP/1.1 200 OK
Content-Type: text/html

And here‘s what an unsuccessful response with a 404 status code looks like:

HTTP/1.1 404 Not Found
Content-Type: text/html

Status codes are grouped into 5 different classes based on their first digit:

  • 1xx Informational
  • 2xx Success
  • 3xx Redirection
  • 4xx Client Error
  • 5xx Server Error

The specific codes and meanings are defined in the HTTP specification RFC 9110 and maintained by the Internet Assigned Numbers Authority (IANA).

As of 2024, there are 63 official status codes registered, although only a handful are commonly used. According to data from W3Techs, the most frequently occurring status codes across the web are:

Status Code Meaning Percent of Requests
200 OK 77.8%
301 Moved Permanently 6.4%
302 Found 4.7%
404 Not Found 4.1%
304 Not Modified 2.1%
400 Bad Request 1.2%
403 Forbidden 1.0%
500 Internal Server Error 0.5%
503 Service Unavailable 0.3%

Together, these top status codes account for over 98% of all responses. Let‘s explore each of the status code classes in more detail and examine the most important codes.

1xx Informational Responses

1xx status codes are rarely encountered in practice, as they are typically handled behind the scenes by the client software. These provisional response codes indicate that the server has received the request headers and is continuing to process the request.

The only 1xx codes in common use are:

  • 100 Continue
  • 101 Switching Protocols
  • 103 Early Hints

For example, a server might send a 100 Continue status in reply to an initial POST request, letting the client know it should proceed to send the body of the request. Or, a 101 Switching Protocols would be used when upgrading the connection from HTTP to WebSocket.

Generally, 1xx codes are non-final responses and will be followed by a final response with a different status code once the request completes. As a developer, you usually don‘t need to explicitly deal with them.

2xx Success Responses

2xx status codes indicate that the client‘s request was received, understood, and accepted by the server. These are the codes you want to see, as they mean everything is working as intended.

The most common success codes are:

  • 200 OK
    • The default code for a successful request. The actual response depends on the request method used. For example, a GET request will return the requested resource in the response body, while a POST request will include the result of the posted data.
  • 201 Created
    • The request succeeded, and a new resource was created as a result. This is typically the code returned after a POST or PUT request that creates a new record in the database.
  • 204 No Content
    • The server successfully processed the request, but is not returning any content in the response body. Often used for DELETE requests, where you want to indicate success but there is no longer a resource to return.

Together, 2xx responses make up the vast majority of web traffic. A 2xx code is a green light letting the client know everything is OK.

3xx Redirection Responses

3xx status codes tell the client that it needs to take an additional action to complete the request, usually because the requested resource has moved to a different URL.

The most frequently used redirection codes are:

  • 301 Moved Permanently
    • The requested resource has been permanently moved to a new URL. The client should update their links and bookmarks. Any future requests for the original URL should use the new URL provided in the response‘s Location header.
  • 302 Found
    • The requested resource has been temporarily moved to a different URL. The client should continue to use the original URL for future requests. 302 is the default code for redirects.
  • 304 Not Modified
    • Indicates that the resource has not been modified since the last time the client requested it. The client can use its cached version rather than re-downloading the resource from the server. Useful for efficiently revalidating cached data.

Redirects are a common and important part of the web. They allow sites to reorganize their URL structure, migrate to new domains, connect related pages, and maintain SEO value.

However, it‘s important to use the right type of redirect and avoid chaining too many together, as this can negatively impact performance and usability.

Search engines have specific guidelines for handling redirects. For example, Google recommends using a 301 for permanent redirects, as this passes the most link equity and maintains search rankings. They treat 302s as temporary and may not update their index. And meta refresh redirects can be seen as manipulative and may incur a penalty. So it‘s important to use redirects thoughtfully and correctly.

4xx Client Error Responses

4xx status codes indicate that there was an error with the client‘s request. Maybe the requested resource doesn‘t exist, the client doesn‘t have permission to access it, or the request was malformed in some way.

Some of the most common client error codes include:

  • 400 Bad Request
    • The server cannot understand or process the request due to a client error, such as a malformed URL, invalid parameters, or wrong content type.
  • 401 Unauthorized
    • The requested resource requires authentication, and the client failed to provide valid credentials. The response must include a WWW-Authenticate header field with instructions on how to authorize.
  • 403 Forbidden
    • The client is authenticated but does not have permission to access the requested resource. Double check your file permissions and user roles to ensure everything is configured correctly.
  • 404 Not Found
    • The famous "page not found" error. The server cannot find the requested resource. Either the URL is incorrect, or the resource has been removed.
  • 429 Too Many Requests
    • The client has sent too many requests in a short period and is being rate limited. Caused by exceeding the API request quota or bot traffic.

4xx errors are frustrating for users and can hurt your site‘s usability, conversion rates, and SEO. According to Ahrefs, over 15% of all websites contain broken links, with an average of 300 dead links per domain! And 404s are the second most frequently encountered HTTP error.

As a best practice, regularly audit your site for 4xx errors and broken links. Use tools like Google Search Console, Ahrefs Site Audit, or Screaming Frog to find and fix them. It‘s also a good idea to create custom branded 404 pages that help the user find what they‘re looking for and match your site‘s look and feel.

When using a 4xx code, make sure you provide a clear error message and explanation in the response body. And avoid using 4xx codes for generic failures – use 500 instead if the fault lies with your application.

5xx Server Error Responses

5xx status codes mean something went wrong on the server side. Even though the request from the client is valid, the server failed to complete it.

The most problematic server error codes are:

  • 500 Internal Server Error
    • The generic catch-all error when the server encounters an unexpected condition and cannot fulfill the request. Usually indicates a problem with the server software or application code.
  • 502 Bad Gateway
    • The server is acting as a proxy or gateway and received an invalid response from the upstream server. Often caused by network issues between servers or when a service is down.
  • 503 Service Unavailable
    • The server is currently unable to handle the request, either because it is overloaded or down for maintenance. Use a 503 when you need to temporarily take your site or service offline.
  • 504 Gateway Timeout
    • Similar to 502, but indicates that the upstream server did not send a response in time. Points to performance or network latency issues.

5xx errors are the most disruptive because they completely prevent visitors from accessing your site or app. According to data from Pingdom, a typical website is down 3 hours per month on average due to 5xx errors. And each hour of downtime can cost businesses hundreds to thousands in lost sales and productivity.

When your site starts returning 5xx errors, it‘s critical to diagnose and resolve the issue ASAP to minimize the impact. Some tips:

  • Set up proactive monitoring and alerts for your web servers and services. Tools like Pingdom, Uptime Robot, or New Relic can notify you immediately when downtime occurs.
  • Have a backup plan in case of an outage. For example, temporarily replacing your site with a static error page, so visitors aren‘t left hanging.
  • Check your server logs and application error tracking to pinpoint the source of 500 errors. Look for any recent deploys, config changes, or spikes in traffic.
  • Scale up server resources or use load balancing to avoid overload during peak traffic.
  • Implement caching, CDNs, and other performance best practices to mitigate issues like 502s and 504s.
  • Communicate with your visitors and keep them in the loop during extended downtime. Post transparent updates on your status page and social media.

Ultimately, the goal is to build resilient infrastructure and monitoring to prevent 5xx errors as much as possible. But having a playbook in place to quickly resolve them is equally important.

The Future of HTTP Status Codes

As we‘ve seen, HTTP status codes remain the bedrock of client-server communication on the web. They provide a shared language for signaling the outcome of requests and maintaining a reliable user experience.

While the core set of status codes has remained relatively stable over the years, there continue to be proposals for new codes to accommodate the evolving ways we build and interact with web applications.

Some of the more recent and notable suggestions include:

  • 428 Precondition Required
    • Indicates that the server requires the request to be conditional, using headers like If-Match or If-Unmodified-Since.
  • 508 Loop Detected
    • Used when the server detects an infinite loop while processing a request, often caused by a circular redirect.
  • 531 Service Unavailable For Legal Reasons
    • Proposed as a more specific version of 403 Forbidden to indicate that the resource is unavailable due to censorship or takedown requests.

However, none of these have been approved as official status codes yet. The IETF HTTPbis working group is responsible for maintaining and updating the HTTP specification and generally prefers to avoid one-off codes in favor of reusing existing ones in a consistent way.

But there is one exciting new development on the horizon: the growing adoption of HTTP/2 and HTTP/3.

These newer versions of the HTTP protocol offer many performance and security enhancements, like multiplexed requests, server push, and baked-in encryption. While they still use the same core status codes for responses, they change other parts of how requests are made (binary vs. plaintext, UDP vs. TCP).

As of 2024, over 70% of web traffic uses HTTP/2, and major browsers are rolling out HTTP/3 support. This means developers will have powerful new communication protocols at their disposal while still relying on the tried-and-true status code system.

Key Takeaways

Let‘s recap the key points about HTTP status codes:

  • Status codes are 3-digit numbers returned by the server to indicate the result of an HTTP request
  • They are grouped into 5 classes: 1xx informational, 2xx success, 3xx redirection, 4xx client error, and 5xx server error
  • Only a handful of status codes make up the majority of web responses, with 200 OK being the most common
  • Redirects (3xx) are widely used to connect URLs but must be applied carefully to avoid SEO and performance issues
  • Client errors (4xx) can frustrate users and hurt your site‘s visibility, so it‘s important to minimize and handle them gracefully
  • Server errors (5xx) cause the most downtime and require prompt alerting and resolution to keep your site running smoothly
  • The HTTP specification continues to evolve with new versions, but the core status code architecture remains in place

Understanding and properly utilizing HTTP status codes is a critical skill for web developers and site owners. By monitoring your site‘s responses, you can ensure that your content is accessible, secure, and presented in the best light to your visitors and search engines.

And when the inevitable error does occur, knowing how to troubleshoot it and communicate clearly with your users can make all the difference in maintaining a trusted, high-performance web presence.

Further Reading

Want to dive deeper into the world of HTTP and web performance? Check out these resources:

Armed with this knowledge, you‘re well on your way to building a faster, more resilient, and error-free web. Happy coding!