Cross-Origin Isolation checker

What is checked

The header trio that governs whether a page can become cross-origin isolated - Cross-Origin-Opener-Policy, Cross-Origin-Embedder-Policy, Cross-Origin-Resource-Policy - along with their Report-Only variants and Origin-Agent-Cluster.

A static check, not a runtime guarantee

This describes only what the main document's own headers declare. Whether a browser actually grants crossOriginIsolated at runtime also depends on every subresource's own CORP/CORS headers, which a static header check on the main document cannot see - a page reported as appearing configured here is not automatically isolated in practice.