TheoriginAgentCluster read-only property of theWindow interface returnstrue if this window belongs to anorigin-keyedagent cluster: this means that the operating system has provided dedicated resources (for example an operating system process) to this window's origin that are not shared with windows from other origins.

Otherwise this property returnsfalse.

Windows that are part of an origin-keyed agent cluster are subjects to some additional restrictions, compared with windows that are not. In particular, they cannot:

• SetDocument.domain, which is a legacy feature that normally allows same-site cross-origin pages to synchronously access each other's DOM.
• SendWebAssembly.Module objects to other same-site cross-origin pages viaWindow.postMessage().
• SendSharedArrayBuffer orWebAssembly.Memory objects to other same-site cross-origin pages.

To request that the browser assign this window to an origin-keyed agent cluster, the server must send theOrigin-Agent-Cluster response header.

Note that the origin-keyed agent cluster feature is only supported insecure contexts. If a site is not a secure context, thewindow.originAgentCluster will always returnfalse.

This page was last modified onApr 3, 2025 byMDN contributors.