Headers Security
medium Severity
Free Check

Cross-Origin Resource Isolation (COOP, COEP, CORP)

Evaluates COOP (Cross-Origin-Opener-Policy) and COEP headers to isolate your browsing context from Spectre-like side-channel attacks.

Test Your Website for Cross-Origin Resource Isolation (COOP, COEP, CORP)

Run this check along with 90+ automated tests across your domain.

Why It Matters

Cross-origin isolation prevents other browser tabs from accessing memory objects and unlocks high-resolution timers (SharedArrayBuffer).

How We Check This

We check for Cross-Origin-Opener-Policy: same-origin and Cross-Origin-Embedder-Policy: require-corp headers.

How to Fix & Implement

Copy-paste configuration blocks tailored for your web server or edge proxy.

nginx snippet
add_header Cross-Origin-Opener-Policy "same-origin" always;
add_header Cross-Origin-Embedder-Policy "require-corp" always;

Frequently Asked Questions

Does COOP prevent tab-nabbing?

Yes. Setting COOP to same-origin severs window.opener references from cross-origin tabs.