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CORS Checker

Check a URL's CORS headers and detect dangerous configurations like Access-Control-Allow-Origin: * with credentials.

Free, unlimited, no signup.

About CORS Checker

CORS is the single most-abused misconfiguration on modern APIs — a wildcard origin combined with credentials effectively hands your authenticated session data to any website on the internet. This checker sends both simple and preflight requests and flags the exact combinations that browsers and pentesters treat as critical findings.

What this tool checks

CORS Checker focuses on the following signals from your site's live response:

  • corsmodule in the full audit
  • headersmodule in the full audit

Why it matters

Signals covered by CORS Checker are the ones attackers, browsers, and search engines look at first. A weak result here means real users are exposed — via downgrade attacks, broken trust warnings, indexing problems, or leaked data — long before anything obvious breaks. Fixing them is usually a config change, not a rewrite, and the impact is immediate.

How to interpret your result

  • Pass — the signal meets modern best practice. Keep it monitored; regressions happen after deploys.
  • Warn — functional but weaker than recommended. Usually a quick header, DNS, or config tweak away from a full pass.
  • Fail — a real risk to users or search visibility. Follow the recommendation shown next to the finding — it's copy-pasteable.

Best practices

  • • Re-run after every deploy — configuration drift is the #1 cause of regressions.
  • • Compare against a competitor's report to spot easy wins.
  • • Wire the public API into CI to gate merges on the score.
  • • Fix warns before failures — they're the cheapest to close and pay off compounding gains.

Frequently asked questions

Yes — we send both simple and preflight requests.

Related guides

Guide

CORS: Cross-Origin Resource Sharing

How CORS actually works, common misconfigurations, and how to lock down Access-Control-Allow-Origin.

Read

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