{
  "entry": {
    "kind": "webmcp",
    "slug": "webmcp-polyfill",
    "name": "WebMCP Polyfill",
    "vendor": "GoogleChromeLabs",
    "description": "The WebMCP Polyfill is a compatibility layer that emulates the experimental WebMCP browser API in browsers that do not yet ship it. WebMCP lets a page declare structured tools — either as annotated HTML forms or as JavaScript functions with JSON schemas — so an AI agent can call them directly instead of guessing at the DOM. The polyfill implements that surface in userland, which is how most sites currently experiment with the API ahead of an origin trial.\n\nThe risk to reason about is not the polyfill's own code so much as what it turns on. Once a page registers tools, any agent driving that browser can enumerate and invoke them inside whatever session the user already has open — logged in, cookied, and authorized. A prompt-injected agent that reaches a page with a `submitOrder` or `transferFunds` tool does not need to defeat authentication; the page has already handed it a typed, documented button. Treat every registered tool as an unauthenticated endpoint reachable by anything that can influence the agent's context.",
    "website": "https://github.com/GoogleChromeLabs/webmcp-polyfill",
    "repository": "https://github.com/GoogleChromeLabs/webmcp-polyfill",
    "documentationUrl": null,
    "license": null,
    "version": null,
    "trustLevel": "official",
    "capabilities": [
      "browser:control",
      "network:outbound"
    ],
    "packaging": null,
    "configFiles": null,
    "category": "library",
    "updatedAt": "2026-09-02",
    "risk": {
      "score": 10,
      "band": "low",
      "signals": [
        {
          "id": "trust-official",
          "kind": "trust",
          "label": "Published by the vendor",
          "contribution": -40
        }
      ],
      "dangerousCombos": []
    },
    "dangerousCombos": []
  }
}