WebMCP Browser Support: Chrome Origin Trial, Polyfill, and What Works Today

Native support: Chrome and Edge, origin trial

Google shipped document.modelContextas a public origin trial starting in Chrome 149 (May 2026), running through Chrome 156. Edge follows Chromium's release schedule and runs the same trial.

In these browsers, WebMCP is a first-class browser API that needs no JavaScript shim or workaround. AI agents that understand WebMCP can query it directly from the browser's own API surface.

The WebMCP polyfill

For every other browser, the WebMCP polyfill (maintained by mcp-b) implements the same document.modelContextAPI in JavaScript. It works by injecting the API surface into the page environment, so AI agents that are aware of WebMCP query the same path regardless of whether it's native or polyfilled.

Aigentably loads the polyfill automatically as part of its snippet. You don't configure anything, and your tools work in every modern browser on day one.

Browser compatibility table

Firefox and Safari

Mozilla and Apple have not announced implementation timelines for WebMCP. The W3C Web Machine Learning Community Group draft is a joint Google/Microsoft submission. Firefox and Safari have expressed interest but not committed.

This doesn't affect your site. The polyfill covers both. When/if native support ships for those browsers, it will be a transparent upgrade: the tool registration code is identical regardless of implementation layer.

What this means for AI agents

AI agent integration with WebMCP depends on the agent, not just the browser. Claude, ChatGPT, and Gemini each have their own integration timelines for querying document.modelContext. Chrome running the native origin trial accelerates this: it's a signal to agent developers that WebMCP is worth building on.

For your site: registering tools now means you're ready when agents query for them. There's no cost to being early.

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