400Bad Request
The server cannot process the request due to malformed syntax.
Common Causes:
Invalid JSON body, missing required parameters, malformed URL, oversized cookies
How to Fix:
Check request body format, validate parameters, review API documentation, clear cookies
401Unauthorized
Authentication is required and has failed or not been provided.
Common Causes:
Missing or expired auth token, invalid credentials, missing API key
How to Fix:
Include valid Authorization header, refresh token, check API key, re-login
403Forbidden
The server understood the request but refuses to authorize it.
Common Causes:
Insufficient permissions, IP blocked, CORS policy, directory listing disabled
How to Fix:
Check user permissions/roles, verify CORS headers, whitelist IP, check file permissions
404Not Found
The requested resource could not be found on the server.
Common Causes:
Wrong URL, deleted resource, typo in path, missing route definition
How to Fix:
Verify URL spelling, check if resource exists, review routing config, check for redirects
405Method Not Allowed
The HTTP method is not supported for this resource.
Common Causes:
Using POST instead of GET (or vice versa), wrong HTTP method for endpoint
How to Fix:
Check API docs for allowed methods, verify request method, check Allow response header
406Not Acceptable
The resource cannot generate content matching the Accept headers.
Common Causes:
Accept header requests unsupported content type, no matching representation
How to Fix:
Adjust Accept header, remove restrictive content negotiation headers
407Proxy Authentication Required
Authentication with the proxy is required.
Common Causes:
Proxy requires credentials, corporate proxy not configured
How to Fix:
Configure proxy credentials, add Proxy-Authorization header
408Request Timeout
The server timed out waiting for the request.
Common Causes:
Slow network, large upload, server too busy, keep-alive timeout
How to Fix:
Retry the request, check network speed, reduce payload size, increase timeout settings
409Conflict
The request conflicts with the current state of the resource.
Common Causes:
Concurrent edits, duplicate entry, version mismatch, resource already exists
How to Fix:
Refresh and retry, use optimistic locking, check for duplicates, use PUT for upserts
410Gone
The resource has been permanently removed.
Common Causes:
API version deprecated, resource intentionally deleted, endpoint retired
How to Fix:
Use the new resource URL, update API version, check migration guide
411Length Required
The Content-Length header is required but not provided.
Common Causes:
Missing Content-Length header on POST/PUT requests
How to Fix:
Add Content-Length header, use chunked transfer encoding
412Precondition Failed
A precondition in the request headers was not met.
Common Causes:
If-Match ETag mismatch, If-Unmodified-Since condition failed
How to Fix:
Fetch latest ETag, refresh resource state, remove conditional headers
413Content Too Large
The request payload is larger than the server allows.
Common Causes:
File upload too large, request body exceeds limit, Nginx/Apache body size limit
How to Fix:
Reduce payload size, compress data, increase server upload limit, use chunked uploads
414URI Too Long
The request URI is longer than the server can process.
Common Causes:
Too many query parameters, long GET request data, redirect loops adding params
How to Fix:
Use POST instead of GET, shorten query parameters, check for redirect loops
415Unsupported Media Type
The media type of the request is not supported.
Common Causes:
Wrong Content-Type header, server does not accept this format
How to Fix:
Set correct Content-Type (e.g., application/json), check API docs for supported formats
416Range Not Satisfiable
The requested range cannot be served.
Common Causes:
Range header beyond file size, invalid byte range
How to Fix:
Verify file size before requesting range, fix Range header values
418I'm a Teapot
The server refuses to brew coffee because it is a teapot (RFC 2324).
Common Causes:
Easter egg, joke response, intentional humorous implementation
How to Fix:
This is a joke status code from the Hyper Text Coffee Pot Control Protocol. No fix needed.
422Unprocessable Content
The request is well-formed but has semantic errors.
Common Causes:
Validation errors, invalid field values, business logic violation
How to Fix:
Check response body for validation errors, fix field values, review API constraints
429Too Many Requests
The user has exceeded the rate limit.
Common Causes:
Too many API calls, rate limit exceeded, aggressive polling
How to Fix:
Implement exponential backoff, check Retry-After header, reduce request frequency, cache responses
431Request Header Fields Too Large
The request headers are too large for the server.
Common Causes:
Too many/large cookies, oversized Authorization header, excessive custom headers
How to Fix:
Clear unnecessary cookies, reduce header size, increase server header limit
451Unavailable For Legal Reasons
The resource is blocked due to legal restrictions.
Common Causes:
Government censorship, DMCA takedown, court order, geo-restriction
How to Fix:
Check applicable laws, use VPN if legally permitted, contact site owner
500Internal Server Error
The server encountered an unexpected condition.
Common Causes:
Unhandled exception, code bug, misconfiguration, dependency failure
How to Fix:
Check server logs, review recent code changes, restart application, check dependencies
501Not Implemented
The server does not support the requested functionality.
Common Causes:
HTTP method not implemented, feature not yet built, unsupported API version
How to Fix:
Use a supported method, check API version, wait for feature implementation
502Bad Gateway
The gateway received an invalid response from upstream.
Common Causes:
Upstream server down, proxy misconfiguration, DNS issues, SSL certificate problem
How to Fix:
Restart upstream server, check proxy config, verify DNS, update SSL certificates
503Service Unavailable
The server is temporarily unable to handle requests.
Common Causes:
Server overloaded, maintenance mode, resource exhaustion, deployment in progress
How to Fix:
Wait and retry, check Retry-After header, scale up resources, check maintenance schedule
504Gateway Timeout
The gateway did not receive a timely response from upstream.
Common Causes:
Upstream server too slow, network timeout, long-running query, resource contention
How to Fix:
Increase timeout settings, optimize slow queries, check upstream health, add caching
505HTTP Version Not Supported
The server does not support the HTTP version in the request.
Common Causes:
Using HTTP/2 on HTTP/1.1-only server, outdated server software
How to Fix:
Use supported HTTP version, update server software
507Insufficient Storage
The server cannot store the representation to complete the request.
Common Causes:
Disk full, storage quota exceeded, database at capacity
How to Fix:
Free up disk space, increase storage quota, clean old data, archive files
508Loop Detected
The server detected an infinite loop while processing.
Common Causes:
Circular references in WebDAV, recursive processing, redirect loops
How to Fix:
Fix circular dependencies, check redirect chains, review WebDAV configuration
511Network Authentication Required
The client needs to authenticate to access the network.
Common Causes:
Captive portal (hotel/airport WiFi), network login page required
How to Fix:
Open browser to authenticate with the network portal, connect to a different network
browserutils
HTTP Error Lookup