Common Client Errors in HTTP
From the HTTP Status Codes cheat sheet · 4xx Client Errors · verified Jul 2026
Common Client Errors
Most frequently encountered client-side errors
javascript
400 : Bad Request - Invalid request syntax
401 : Unauthorized - Authentication required
403 : Forbidden - No permission to access
404 : Not Found - Resource doesn't exist
405 : Method Not Allowed - HTTP method not supported
409 : Conflict - Request conflicts with state🔐 401 = not authenticated, 403 = not authorized
❌ 400 for validation errors and malformed JSON
📌 404 for missing resources or endpoints
⚠️ 409 for duplicate resources or version conflicts