When you're deep in a coding session and encounter a mysterious 404 or that dreaded 500 error, you're dealing with HTTP status codes. These three-digit numbers are your server's way of communicating what happened when someone tried to access your website. Think of them as standardised messages between your server and browsers - essential intelligence that can make or break your user experience.

What Are HTTP Status Codes?

HTTP status codes are three-digit numeric codes issued by a server in reply to a browser request. They're sent from the server to the client (typically a browser or an API consumer) after a request is made. Every time someone clicks a link or types in a URL, your server processes the request and responds with both the requested content and a status code.

The beauty of this system lies in its simplicity. These codes are divided into 5 "classes" based on their function, with each category serving a unique purpose and impact on site behaviour, user experience, and SEO.

The Five Categories of Status Codes

1xx - Informational Responses

1xx status codes are informational responses indicating that the client's request has been received and the server is continuing the process. These are rarely seen by end users but are crucial for ongoing server processes.

• 100 Continue: Server received request headers, ready for the request body
• 101 Switching Protocols: Server is changing protocols as requested
• 103 Early Hints: Server suggests resources for preloading whilst preparing the final response

2xx - Success Codes

The golden category every developer wants to see. 200s: Success codes returned when browser request was received, understood, and processed by the server.

• 200 OK: The standard response for successful requests - everything worked perfectly
• 201 Created: New resource successfully created (common in API responses)
• 204 No Content: Request successful but no content to return

3xx - Redirection Codes

300s: Redirection codes returned when a new resource has been substituted for the requested resource. These tell the client that further action is needed.

• 301 Moved Permanently: Resource permanently moved to new URL (crucial for SEO)
• 302 Found: Temporary redirect to different URL
• 304 Not Modified: Client's cached version is still valid

4xx - Client Error Codes

400s: Client error codes indicating that there was a problem with the request. These suggest the issue lies with the request itself.

• 400 Bad Request: Server cannot process due to client-side error
• 401 Unauthorised: Authentication required
• 403 Forbidden: Server understood request but refuses to authorise it
• 404 Not Found: The infamous "page not found" error
• 429 Too Many Requests: Rate limiting in effect

5xx - Server Error Codes

500s: Server error codes indicating that the request was accepted, but that an error on the server prevented the fulfillment of the request. These point to server-side issues.

• 500 Internal Server Error: Generic server error
• 502 Bad Gateway: Invalid response from upstream server
• 503 Service Unavailable: Server temporarily unable to handle requests
• 504 Gateway Timeout: Upstream server didn't respond in time

Why Status Codes Matter for Developers

Debugging Made Easier

Knowing the status codes of your web pages helps you identify and resolve issues like broken links (404 errors) or server-side problems (500 errors). Instead of guessing what went wrong, status codes provide immediate insight into where the problem lies.

API Development

API status codes are vital in error handling and debugging when building web services or applications. Standardised responses help front-end developers and testers identify whether the issue is on the client, server, or within the API gateway.

Performance Monitoring

Running into HTTP errors like 404 or 500 is more than just an inconvenience, it can affect your users' experience and your site's performance. Regular monitoring helps catch issues before they impact users.

SEO and User Experience Impact

Search engines treat status codes as critical signals. 301: Signals a permanent change. Good for maintaining SEO authority. 302: Temporary redirect. Avoid overuse, as it doesn't pass SEO value. 404: Indicates missing content.

From an SEO standpoint, status codes directly affect crawlability, indexing, and page experience. Frequent 5xx errors may lead to deindexing, while excessive 404s signal poor user experience.

Monitoring Your Status Codes

Browser Developer Tools

Most browsers include built-in tools for checking status codes. Open Developer Tools, navigate to the Network tab, and reload your page to see all HTTP responses.

Command Line Tools

For developers, cURL provides quick status code checks:

curl -I https://yourwebsite.com

Automated Monitoring

Listening to HTTP Status codes is a great way to get a good indication of the health of a site or server. This is where comprehensive monitoring becomes essential.

Best Practices for Handling Status Codes

1. Use Appropriate Codes: Don't return 200 OK for errors or 404 for temporary issues
2. Implement Proper Redirects: Use 301 for permanent moves, 302 for temporary ones
3. Monitor Regularly: Set up alerts for 4xx and 5xx errors
4. Provide Meaningful Error Pages: Don't leave users with generic error messages
5. Log Everything: Keep detailed logs of status codes for analysis

Common Pitfalls to Avoid

• Returning 200 OK for soft errors (like "user not found" in API responses)
• Using 302 redirects when 301 is more appropriate for SEO
• Ignoring 5xx errors thinking they'll resolve themselves
• Not customising error pages to maintain brand consistency
• Failing to set up proper monitoring and alerting

Status codes are fundamental to web communication. They provide the feedback loop that keeps your applications running smoothly and your users informed. Whether you're building APIs, debugging production issues, or optimising for search engines, understanding and properly implementing HTTP status codes is non-negotiable.

Remember: every status code tells a story. The question is whether you're listening to what your server is trying to tell you.

Ready to take control of your website's health?

Metrics+ monitors all HTTP status codes across your entire site, giving you up to 12 months of detailed log retention so you can spot patterns and fix issues before they impact your users. See our monitoring plans and subscribe today to ensure your status codes are always telling the right story.