HTTP Status Codes

Instant HTTP status code reference. Search 1xx-5xx REST API response codes, RFC 9110 specs, cache headers, and quick code fixes. Fast client-side search.

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In-Depth Technical Guide

HTTP Status Codes & REST API Design: Complete Error Handling Architecture

Master HTTP response status codes for scalable RESTful APIs. Detailed architectural patterns for 2xx success, 3xx redirects, 4xx client errors, and 5xx server failures.

Read Full Guide (8 min read)

Technical Overview: How HTTP Status Codes Works

HTTP Status Codes is a comprehensive RFC 9110 and RFC 9111 reference directory and client simulator covering 1xx (Informational), 2xx (Success), 3xx (Redirection), 4xx (Client Errors), and 5xx status codes (HTTP code 5xx server error responses). Search any web status code to inspect definitions, default cacheability rules, status comparisons, and client response handlers.

Catalogs standard HTTP status codes governed by RFC 9110 (HTTP Semantics) and RFC 9111 (HTTP Caching), along with common platform extensions (Cloudflare 520-527). Identifies RFC default cacheability flags, required response headers (Location, WWW-Authenticate, Retry-After), architectural nuances (301 vs 308, 401 vs 403, 404 vs 410, 502 vs 504), and provides simulated Fetch and Axios handler code for both 4xx client errors and 5xx response codes.

Practical Examples & Usage

Diagnosing HTTP Code 5xx Server Response Codes (502 Bad Gateway vs 504 Gateway Timeout)

Input:Code: 502 Bad Gateway vs 504 Gateway Timeout

Output:

502: Upstream application server returned invalid response | 504: Upstream server failed to respond within gateway timeout threshold

Helps backend engineers and DevOps diagnose whether an upstream application process crashed (502) or suffered a slow database query or network timeout (504).

Web Status Code 500 Internal Server Error & 5xx Status Codes Handling

Input:Code: 500 Internal Server Error

Output:500 Internal Server Error | Type: Server Error (5xx) | Cacheable: No | RFC 9110

Standard catch-all response code for unexpected server crashes; should include structured problem details (RFC 7807) without exposing sensitive database or internal stack traces.

Lookup HTTP 429 Too Many Requests

Input:Code: 429

Output:

429 Too Many Requests (RFC 6585) | Type: Client Error | Cacheable: No | Meaning: Rate limit exceeded. Include `Retry-After` header indicating wait seconds.

Provides formal specification definition, error category, cacheability rules, and recommended API response headers.

Real-World Applications & Use Cases

Diagnosing HTTP code 5xx server error codes (500 Internal Server Error, 502 Bad Gateway, 503 Service Unavailable, 504 Gateway Timeout) behind reverse proxies and CDNs.
Selecting appropriate 5xx status codes or 4xx client error codes when designing REST and GraphQL APIs (e.g., 201 Created vs 202 Accepted).
Looking up any web status code definition and RFC compliance rules during frontend and backend debugging.
Troubleshooting authentication errors (401 Unauthorized vs 403 Forbidden, 404 Not Found vs 410 Gone).
Configuring correct SEO redirection codes (301 Permanent vs 302 Temporary vs 308 Permanent Redirect).

How to use HTTP Status Codes

Filter codes by number (e.g., 404, 429) or keyword in the real-time search field.
Filter by category (1xx, 2xx, 3xx, 4xx, 5xx) or enable "Cacheable Only".
Click any status card to view its RFC specification, cacheability, and real-world developer guidance.
Explore the "Nuances & Comparisons" tab to understand differences like 301 vs 308 or 401 vs 403.
Use the "Client Response Simulator" to preview fetch/axios response objects and sample code.

Edge Cases & Limitations

•Certain proprietary codes (e.g. Cloudflare 520-527, Nginx 499) are platform-specific extensions outside official IETF RFCs.
•301 and 308 redirects are cached permanently by browsers; use 302 or 307 during development to prevent accidental local cache lockouts.
•401 requires a WWW-Authenticate header in the response, whereas 403 indicates authentication succeeded but authorization was denied.

Recommended Best Practices

•Use 308 instead of 301 when redirecting API endpoints to ensure HTTP POST and PUT request bodies and methods are preserved.
•Include machine-readable problem details (RFC 7807) in 4xx and 5xx error response payloads.
•Always supply a Retry-After header with 429 (Too Many Requests) and 503 (Service Unavailable) responses.

Data Handling Profile

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Network Transmission: Tool inputs and calculation results are processed in browser memory and are not uploaded to Outlivo application servers.

Frequently Asked Questions

What causes HTTP code 5xx server errors and how do I fix them?

HTTP code 5xx responses (such as 500 Internal Server Error, 502 Bad Gateway, 503 Service Unavailable, and 504 Gateway Timeout) indicate that the server encountered an unexpected failure fulfilling a valid request. Common causes include unhandled exceptions, reverse proxy connection drops, backend database timeouts, and server resource exhaustion.

What is the difference between 4xx client errors and 5xx response codes?

A 4xx web status code indicates a client-side problem (such as invalid query syntax, expired authentication tokens, or missing resources like 404). In contrast, 5xx status codes indicate backend infrastructure issues where the server failed to process a valid client request.

What are the main differences between 301, 302, 307, and 308 redirects?

301 and 308 are permanent redirects that transfer SEO PageRank; 302 and 307 are temporary. Historically, 301 and 302 allowed browsers to change POST requests to GET. RFC 9110 standards 307 and 308 strictly preserve the original HTTP method and body across redirects.

What is the precise difference between 401 Unauthorized and 403 Forbidden?

HTTP 401 means "Unauthenticated": the client did not supply valid authentication credentials. HTTP 403 means "Forbidden": the server authenticated the user identity, but the account permissions refuse access to the resource.

Which HTTP status codes are cacheable by default?

Under RFC 9110 and RFC 9111, responses with status codes 200, 203, 204, 206, 300, 301, 404, 405, 410, 414, and 501 are inherently cacheable unless explicit Cache-Control headers (like no-store) override them.

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