HTTP
426 Upgrade Required
The server refuses to perform the request using the current protocol but might after the client upgrades to a different protocol.
When You See This Code
When a server requires HTTPS or a newer protocol version.
How to Fix
Switch to the protocol specified in the Upgrade response header.
Specification
View RFC / Specification →Guides
Understanding HTTP Status Codes: A Complete Guide
HTTP Fundamentals
HTTP Redirects: 301 vs 302 vs 307 vs 308
HTTP Fundamentals
HTTP Caching: Cache-Control, ETags, and 304 Responses
HTTP Fundamentals
Choosing the Right HTTP Status Codes for REST APIs
API Design
gRPC Status Codes: A Practical Guide
API Design
Debugging 502 Bad Gateway Errors
Debugging & Troubleshooting
Debugging CORS Errors: A Developer's Guide
Debugging & Troubleshooting
Debugging Timeout Errors: 408 and 504
Debugging & Troubleshooting
401 Unauthorized vs 403 Forbidden: When to Use Each
Security & Authentication
Essential HTTP Security Headers
Security & Authentication
Complete Guide to HTTP Methods: GET, POST, PUT, PATCH, DELETE
HTTP Fundamentals
Essential HTTP Headers Every Developer Should Know
HTTP Fundamentals
HTTP/2 vs HTTP/3: What Changed and Why
HTTP Fundamentals
How to Implement and Handle Rate Limiting (429)
API Design
API Versioning Strategies: URL, Header, and Query Param
API Design
Designing Consistent API Error Responses
API Design
Debugging 503 Service Unavailable Errors in Production
Debugging & Troubleshooting
TLS/SSL Certificate Troubleshooting Guide
Debugging & Troubleshooting
OAuth 2.0 Flows Explained: Authorization Code, Client Credentials, PKCE
Security & Authentication
JSON Web Tokens: Structure, Signing, and Common Pitfalls
Security & Authentication
API Keys vs OAuth vs JWT: Choosing the Right Auth Method
Security & Authentication