In this guide, we'll dive into the world of HTTP status codes, explaining what they are, how they’re grouped, and what the most common ones mean.
What Are HTTP Status Codes?
HTTP status codes are standardized responses sent by a server to indicate the outcome of a client’s request. When your browser or an API client makes a request to a server (like visiting a website or submitting a form), the server responds with a status code as part of the HTTP response.
These codes provide a quick way to know whether the request was successful, redirected, failed due to a client-side error, or failed due to a server-side issue.
Categories of HTTP Status Codes
HTTP status codes are grouped into five categories based on the first digit:
- 1xx – Informational
- 2xx – Success
- 3xx – Redirection
- 4xx – Client Error
- 5xx – Server Error
Let’s explore each category in detail.
1xx – Informational Codes
These codes indicate that the request was received and the process is continuing.
- 100 Continue: The server has received the request headers and is waiting for the body.
- 101 Switching Protocols: The client has requested to switch protocols and the server has agreed.
These are rarely seen in everyday development but play a role in complex HTTP exchanges.
2xx – Success Codes
This group means the request was successfully received, understood, and accepted.
- 200 OK: The standard success response.
- 201 Created: The request was successful and a new resource was created.
- 204 No Content: The request was successful, but there's no content to return.
These are the most desirable status codes during development and API testing.
3xx – Redirection Codes
Redirection codes tell the client that further action is needed to complete the request.
- 301 Moved Permanently: The resource has a new permanent URI.
- 302 Found: The resource is temporarily located at a different URI.
- 304 Not Modified: The client’s cached version of the resource is still valid.
These are essential for SEO, content delivery, and browser caching mechanisms.
4xx – Client Error Codes
These codes signal that there was an issue with the request made by the client.
- 400 Bad Request: The request cannot be processed due to malformed syntax.
- 401 Unauthorized: Authentication is required and has either failed or not been provided.
- 403 Forbidden: The server understands the request but refuses to authorize it.
- 404 Not Found: The requested resource could not be found.
Client error codes are especially important for debugging frontend or API requests.
5xx – Server Error Codes
Server errors indicate that the request was valid, but the server failed to fulfill it.
- 500 Internal Server Error: A generic error when the server fails unexpectedly.
- 502 Bad Gateway: The server received an invalid response from an upstream server.
- 503 Service Unavailable: The server is temporarily overloaded or under maintenance.
- 504 Gateway Timeout: The server didn’t get a timely response from another server.
These errors often require server-side debugging and infrastructure checks.
Why HTTP Status Codes Matter
HTTP status codes are not just technical details — they’re vital for:
- Debugging: Identify the root cause of a failed request quickly.
- Monitoring: Track service health and downtime with automated tools.
- API Development: Ensure consistent responses and client communication.
- SEO: Search engines interpret 301 and 404 codes to index pages accurately.
By paying attention to HTTP status codes, developers and DevOps teams can resolve issues faster and build more reliable systems.
Tips for Working with HTTP Status Codes
- Always log responses: Include status codes in logs for easier troubleshooting.
- Use proper status codes in APIs: A 200 OK for a failed login is misleading—use 401 Unauthorized instead.
- Customize error messages: Help users and developers by providing context with the status code.
- Monitor with tools: Use API monitors, server logs, and tools like Postman or curl to analyze status codes.
Conclusion
HTTP status codes are the backbone of communication on the web. They help you understand what’s happening behind the scenes of every web request. From debugging API issues to maintaining server health and optimizing SEO, status codes are powerful tools every developer and tester should understand.
Start paying closer attention to these three-digit codes—they’re your first clue in diagnosing and fixing issues fast.
Read more on https://keploy.io/blog/community/understanding-http-status-codes