What Is the HTTP Status Code Lookup Tool?
The HTTP Status Code Lookup is an instant, browser-based reference tool designed for web developers, API designers, DevOps engineers, and system administrators. HTTP response status codes are three-digit integers issued by a web server in response to a client's request made to the server. They communicate whether an operation succeeded, required redirection, failed due to client error, or crashed on the server.
This tool provides complete, offline explanations, standard RFC references, common practical use cases, and best-practice developer notes for every major status code from 100 to 524, including prominent non-standard edge codes from Nginx and Cloudflare.
How to Search and Filter HTTP Response Codes
- Filter by Range: Click category filter pills (1xx, 2xx, 3xx, 4xx, 5xx) to quickly isolate informational messages, successful transactions, redirects, or errors.
- Keyword Search: Type any numerical code (e.g.
429), reason phrase (e.g.Gateway Timeout), or technical term (e.g.cache,websocket,rate limit) into the search bar. - Review Details: Inspect the official RFC reason phrase, category classification, concise technical explanation, realistic API use case, and developer guidance.
- Copy Code: Click Copy Code on any card to copy the status code number directly to your clipboard for documentation or commit messages.
Essential HTTP Codes at a Glance
200 OK • 201 Created • 204 No Content
Indicates successful fulfillment. 200 is standard for GETs; 201 marks newly created REST resources; 204 represents successful DELETE operations with no return body.
301 Moved Permanently • 304 Not Modified
Redirections and caching signals. 301 migrates SEO link authority permanently; 304 enables browsers to serve assets from local cache without re-downloading.
400 Bad Request • 401 Unauthorized • 404 Not Found
Client-side faults. 400 flags validation syntax bugs; 401 denotes missing authentication; 404 confirms the endpoint or database record does not exist.
500 Internal Server Error • 502 Bad Gateway
Origin and upstream failures. 500 signals unhandled code crashes; 502 occurs when a reverse proxy like Nginx fails to reach the application backend daemon.
Key Features of CodeCrate HTTP Status Code Lookup
Instant Local Lookups
Runs 100% offline with zero external network overhead. Results filter instantaneously as you type.
Clear Standard Labels
Clearly distinguishes official IETF RFC standards from widely deployed reverse-proxy codes (e.g. Nginx 499, Cloudflare 520–524).
Actionable Developer Notes
Every code includes practical tips covering header requirements, REST semantics, and Core Web Vitals optimization.
Categorized Color Badges
Color-coded status badges provide immediate visual recognition across 1xx, 2xx, 3xx, 4xx, and 5xx response groups.
Common Web & API Development Use Cases
- RESTful API Design: Selecting the semantically accurate status code for endpoint errors, form validations, and asynchronous queue ingestion (e.g. 202 Accepted vs 201 Created).
- Debugging Production Errors: Interpreting server error logs (502 Bad Gateway vs 504 Gateway Timeout) to isolate whether an issue lies in the reverse proxy or slow database queries.
- SEO & URL Migration: Choosing between 301 Permanent Redirects for canonical domain upgrades and 302 Found for temporary maintenance windows.
- Rate Limiting & Security: Implementing 429 Too Many Requests with
Retry-Afterheaders to guard public endpoints against brute-force attacks and abuse.
Technical Notes & RFC Best Practices
When building modern web services conforming to RFC 9110 (HTTP Semantics), observe the following principles:
- Never Return 200 with an Error Payload: Returning
{ "status": "error", "message": "Failed" }inside a 200 OK breaks client HTTP interceptors, caching layers, and APM monitors. Use 4xx or 5xx codes. - Include WWW-Authenticate for 401s: RFC 9110 specifies that a 401 response must include a
WWW-Authenticatechallenge header describing the required authentication scheme (e.g.Bearer realm="api"). - Use 422 for Semantic Validation Failures: When JSON syntax is well-formed but violates business validation rules (e.g. duplicate username, age below minimum), return 422 Unprocessable Content.
- Respect 204 Body Constraints: A 204 No Content response must never include a response body. Including bytes in a 204 is an HTTP specification violation.
Frequently Asked Questions
What is the difference between 401 and 403?
401 Unauthorized means the request lacks valid authentication credentials. 403 Forbidden means the identity is verified, but access is refused due to insufficient permissions.
What causes a 502 Bad Gateway error?
A 502 error occurs when an edge proxy (such as Nginx, Cloudflare, or AWS ALB) receives an invalid response, connection reset, or abrupt socket close from your application backend server.
What is HTTP status code 418?
HTTP 418 "I'm a teapot" is an April Fools' joke defined in RFC 2324 (HTCPCP). While not intended for production systems, it is widely implemented by developers as an easter egg.
What does 304 Not Modified mean?
304 indicates that the resource has not changed since the client's last conditional request (via ETag or If-Modified-Since). The browser safely displays its cached copy.
Are Cloudflare 520–524 errors official HTTP standards?
No. Codes 520 through 524 are proprietary edge error codes created by Cloudflare to diagnose connectivity issues between Cloudflare's network and customer origin servers.
Can I copy status code numbers directly?
Yes. Simply click the Copy Code button on any status card to copy the 3-digit number straight to your clipboard.