ValidateThis

CORS preflight checker

Related tools

Validators and utilities that complement CORS preflight checker — same session, no sign-up.

Paste OPTIONS response headers plus Origin and method: checks Allow-Origin, credentials, methods, headers, Max-Age. Heuristic only — confirm in browser.

Paste OPTIONS response headers from DevTools (or a proxy). Add the browser Origin and method you intend to use. This is a static checklist, not a live browser preflight.

How to use this tool

  1. Paste your sample in the input (or fetch from URL if this tool supports it).
  2. Run the main action on the page to execute CORS preflight checker.
  3. Read the result, fix the source data or config, and re-run if needed.

What this check helps you catch

  • Paste OPTIONS response headers plus Origin and method: checks Allow-Origin, credentials, methods, headers, Max-Age. Heuristic only — confirm in browser.
  • Limits called out in the description (what this tool does not verify — e.g. live network reachability, issuer databases, or strict schema contracts unless stated).
  • Structural or syntax mistakes that would break parsers, serializers, or the next step in your workflow.

FAQ

What does CORS preflight checker do?
Paste OPTIONS response headers plus Origin and method: checks Allow-Origin, credentials, methods, headers, Max-Age. Heuristic only — confirm in browser. Use the form above, then see “How to use” and “What this check helps you catch” for behavior detail.
Is this a substitute for server-side validation?
No. Use it for manual checks and triage; production systems should still validate and authorize on the server.
Where does processing happen?
Most validators here run in your browser. If a tool calls an API, that is stated on the page. See the site privacy policy for data handling.