Why does wildcard origin break when credentials are enabled?
Browsers reject credentialed CORS responses when Access-Control-Allow-Origin is `*`, so you must return a specific origin.
CORS Header Generator
Generate Access-Control-* headers for API and preflight responses
API & HTTP
π 100% client-side β your data never leaves this pagePage mode
CORS Policy Inputs
Quick CTA
Start with Origin, methods, and headers to generate copy-ready CORS response headers immediately; preflight scenarios stay in Deep.
Output
Generated CORS headers appear here
100% client-side
Page reading mode
Quick keeps the summary, direct answers, and next steps so you can validate fit and get a result faster.
About this tool
CORS Header Generator helps backend and gateway teams build correct Access-Control-* response headers quickly. Configure allowed origin strategy, methods, request headers, exposed headers, credentials, and preflight max-age, then copy ready-to-use output for servers or reverse proxies. The generator also enforces an important rule: when credentials are enabled, wildcard origin is invalid in browsers. This tool is useful for debugging frontend-to-API calls, fixing preflight failures, and producing safe CORS policies that are strict enough for production. All logic runs client-side and your inputs never leave the browser.
Direct Answers
When should I add Vary: Origin?
Add it when you dynamically reflect origins or return different CORS headers per request, so shared caches do not reuse the wrong response.
Suggested Workflow
CORS Credentials + Wildcard Origin Error: Practical Fix Guide
Fix the classic browser CORS block when credentials are enabled with Access-Control-Allow-Origin=*.
SameSite=None Requires Secure: Cookie Fix Playbook
Resolve cross-site login/session failures caused by cookie attribute mismatch in modern browsers.
Cache-Control no-store + max-age Conflict: How to Fix Caching Chaos
Diagnose and resolve contradictory cache directives that cause random hit/miss behavior.