Developer Tools100% In-Browser Privacy4.9 / 5

HTTP Status Code Lookup & Debugging Guide

Search and explore every HTTP response code defined in IETF RFC specifications, understand underlying causes, and view actionable developer solutions.

No Watermarks

Zero Server Uploads

Last updated: September 7, 2026

200OK

2xx

The standard response for successful HTTP requests. The payload depends on the request method.

Common Cause: Normal successful response for GET, POST, or PUT.

How to Fix: No action required. Everything operated as intended.

201Created

2xx

The request has succeeded and led to the creation of one or more new resources.

Common Cause: Typically returned after a successful POST request creating a user, record, or order.

How to Fix: Read the Location header or response body to fetch the newly created resource identifier.

204No Content

2xx

The server successfully processed the request, but is not returning any content.

Common Cause: Common in DELETE operations or POST actions where the client doesn't need to leave the current page.

How to Fix: Client should not expect a response body or JSON payload.

301Moved Permanently

3xx

The target resource has been permanently assigned a new URI and future references should use it.

Common Cause: Domain migration, URL structure overhaul, or HTTP to HTTPS redirect.

How to Fix: Update bookmarks, internal links, and API client URLs to point to the new location provided in the header.

302Found (Temporary Redirect)

3xx

The target resource temporarily resides under a different URI. Future requests should still use the original URI.

Common Cause: Temporary maintenance redirects, geo-location routing, or login authentication flows.

How to Fix: Follow the Location header temporarily without changing permanent canonical references.

304Not Modified

3xx

Indicates that the resource has not been modified since the version specified by the request headers.

Common Cause: Client sent If-Modified-Since or If-None-Match headers and the server's cache validation matched.

How to Fix: The browser or client should serve the cached copy locally to save bandwidth.

307Temporary Redirect

3xx

Same semantics as 302, but guarantees the HTTP method (e.g. POST) is not changed when following the redirect.

Common Cause: Preserving form submission POST payloads across temporary endpoint changes.

How to Fix: Re-issue the exact same HTTP request and body to the new Location URI.

308Permanent Redirect

3xx

Same semantics as 301, but guarantees the HTTP method is not altered on redirect.

Common Cause: Permanent API endpoint version migrations.

How to Fix: Permanently update all client configurations with the new URL.

400Bad Request

4xx

The server cannot or will not process the request due to an apparent client error (malformed syntax).

Common Cause: Invalid JSON body, missing required fields, or illegal query parameters.

How to Fix: Inspect the payload syntax, validate JSON structures, and check the server response body for validation error messages.

401Unauthorized

4xx

The request has not been applied because it lacks valid authentication credentials for the target resource.

Common Cause: Missing, invalid, or expired Authorization Bearer token, session cookie, or API key.

How to Fix: Log in again, refresh OAuth access tokens, or verify the API key in the request headers.

403Forbidden

4xx

The server understood the request but refuses to authorize it. Unlike 401, authentication makes no difference.

Common Cause: The authenticated user does not have sufficient role permissions (e.g., non-admin accessing admin routes), or IP firewall block.

How to Fix: Check user role access levels (RBAC) or verify Cloudflare/WAF IP whitelist rules.

404Not Found

4xx

The server cannot find the requested resource. Links that lead here are typically broken or dead links.

Common Cause: Typo in the URL, deleted product/post, or route not defined in router table.

How to Fix: Double-check the URL slug, verify route definitions in Next.js/Express, or configure a custom 301 redirect if deleted.

405Method Not Allowed

4xx

The request method is known by the server but is not supported by the target resource.

Common Cause: Sending a POST request to an endpoint that only accepts GET requests.

How to Fix: Inspect the endpoint's Allow header to verify accepted methods (e.g. GET, POST, PUT, DELETE).

408Request Timeout

4xx

The server timed out waiting for the request from the client.

Common Cause: Slow network connection, large file upload stalled, or client closed connection mid-stream.

How to Fix: Retry request or optimize network latency.

409Conflict

4xx

Indicates that the request could not be processed because of conflict in the current state of the resource.

Common Cause: Attempting to create an account with an existing email, or concurrent edits in database.

How to Fix: Resolve the conflicting duplicate record or use optimistic locking retry loops.

410Gone

4xx

The target resource is no longer available at the origin server and no forwarding address is known.

Common Cause: Permanent intentional deletion of content or sunsetted API v1 endpoints.

How to Fix: Remove links and tell search engines to de-index the URL immediately.

413Payload Too Large

4xx

The request entity is larger than limits defined by the server.

Common Cause: Uploading an image, PDF, or video that exceeds the Nginx client_max_body_size or serverless limit.

How to Fix: Increase max body size in reverse proxy or compress files in the browser before sending.

422Unprocessable Content

4xx

The server understands the content type, and the syntax is correct, but was unable to process the contained instructions.

Common Cause: Semantic validation failure (e.g., age is a negative number or email is formatted incorrectly).

How to Fix: Correct the individual field values flagged in the validation error response.

429Too Many Requests

4xx

The user has sent too many requests in a given amount of time ('rate limiting').

Common Cause: Exceeded API rate limits, rapid polling, or automated scraper detection.

How to Fix: Inspect the Retry-After header, implement exponential backoff, or upgrade API plan quota.

500Internal Server Error

5xx

A generic error message, given when an unexpected condition was encountered and no more specific message is suitable.

Common Cause: Unhandled exception in backend code, database crash, or broken environment variables.

How to Fix: Check backend server application logs (Sentry, Datadog, CloudWatch) for stack traces.

502Bad Gateway

5xx

The server, while acting as a gateway or proxy, received an invalid response from the inbound server it accessed.

Common Cause: Node.js/Python backend process crashed or stopped listening on port 3000 behind Nginx/Cloudflare.

How to Fix: Restart the upstream backend service, verify PM2/systemd process status, and test localhost connectivity.

503Service Unavailable

5xx

The server is not ready to handle the request. Common causes are server maintenance or severe traffic overload.

Common Cause: High CPU/memory exhaustion, scheduled maintenance window, or downstream database outage.

How to Fix: Scale up compute instances, enable auto-scaling, or inspect Retry-After header.

504Gateway Timeout

5xx

The server, while acting as a gateway or proxy, did not receive a timely response from an upstream server.

Common Cause: Slow database query, external API hanging, or compute task taking longer than proxy timeout (typically 30s or 60s).

How to Fix: Optimize database queries, offload long-running tasks to background queues, or increase proxy timeout.

HTTP Status Code Ranges

HTTP status codes are standardized three-digit integers returned by web servers to indicate whether a specific HTTP request was successfully completed:

1xx (Informational): Request received, continuing process (e.g. 101 Switching Protocols).
2xx (Success): Action was successfully received, understood, and accepted (e.g. 200 OK, 201 Created).
3xx (Redirection): Further action must be taken to complete request (e.g. 301 Moved Permanently, 304 Not Modified).
4xx (Client Error): Request contains syntax error or cannot be fulfilled (e.g. 400 Bad Request, 404 Not Found, 429 Too Many Requests).
5xx (Server Error): Server failed to fulfill an apparently valid request (e.g. 500 Internal Server Error, 502 Bad Gateway).

How to Use HTTP Status Code Lookup & Debugging Guide (Step-by-Step)

Type a status code (e.g. 502) or error name into the search bar.

Filter by category tabs (2xx Success, 3xx Redirection, 4xx Client Error, 5xx Server Error).

Read the formal RFC summary, common root causes, and recommended fixes.

Applications

Common Use Cases

Look up unfamiliar HTTP error codes returned by APIs or web servers.
Understand the difference between 301 and 302 redirects or 401 and 403 errors.
Follow step-by-step developer troubleshooting fixes for 502 Bad Gateway and 504 Gateway Timeout.

Privacy Guarantee

Zero Server Uploads

Unlike traditional online converters that upload your confidential documents to external cloud servers, MultiToolX executes computations in your browser runtime via HTML5 Canvas, Web Crypto, and WebAssembly.

Your data never leaves your device and cannot be viewed, stored, or harvested by anyone.

Companion Step-by-Step Guide

Understanding HTTP Status Codes: 200, 301, 404, 500, 502 & Debugging Guide

A complete guide to HTTP status codes, explaining client errors vs server crashes, redirect mechanisms, and debugging 502 Bad Gateway errors.

Read Full Guide

FAQ

Frequently Asked Questions

What causes a 502 Bad Gateway error?

A 502 error occurs when a reverse proxy (like Nginx, Cloudflare, or AWS ALB) receives an invalid response or connection drop from the upstream origin server (e.g., Node.js or Python backend).

What is the difference between 401 Unauthorized and 403 Forbidden?

401 means authentication is required and missing or invalid. 403 means authentication succeeded, but the user does not have permission to access the requested resource.

When should I use a 301 vs a 302 redirect?

Use 301 for permanent URL changes (transfers SEO link equity). Use 302 for temporary routing (does not change canonical indexation in Google).

Free Webmaster Widget

Embed the HTTP Status Code Lookup & Debugging Guide on Your Website or Blog

Enhance your articles and give your visitors a fast, 100% free browser utility with zero installation. Copy our responsive iframe code with one click.

Explore More