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# Cross-Origin isolation checker

Reads COOP, COEP, CORP, their Report-Only twins and Origin-Agent-Cluster for one URL through the proxy and reports isolation readiness, stating plainly that a static header check cannot prove runtime isolation.

Press the button to read the headers
Nothing leaves this page until you do. The report grades COOP, COEP, CORP, their Report-Only twins, and Origin-Agent-Cluster on the main document, and states plainly what a static check cannot prove.

A passing result here is not a runtime guarantee. This reads the main document's response headers only. A browser grants crossOriginIsolated at runtime only when every subresource also passes its CORP or CORS check, which a header fetch cannot see. To confirm the real thing, load the page and check self.crossOriginIsolated in its own console.
Options

## More network tools

- [HTTP header parser](/web/headers)
[All network tools](/network)

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Canonical HTML: https://nutter.tools/network/cross-origin-isolation-checker
Markdown version: https://nutter.tools/network/cross-origin-isolation-checker.md
Plain-text version: https://nutter.tools/network/cross-origin-isolation-checker.txt
Agent index: https://nutter.tools/llms.txt