WebMCP — how to make your site agent-ready

What it is

WebMCP brings the MCP contract into the browser. A page declares tools via a <script type="application/mcp+json"> block or the window.mcp API. Chrome's WebMCP EPP (Early Preview Proposal) gives agents (like the one inside Chrome) direct access to page-scoped tools.

It's complementary to server-side MCP: WebMCP exposes capabilities that make sense only while the user is on the page (e.g. "summarise this article", "add this item to my cart using my logged-in session").

Remediation Prompt

I want to improve my site's agent readiness. Please implement the following fix for WebMCP across our codebase.

Instructions:
Please fix the WebMCP issue on my site so it is agent-ready.

How we test it

Since V1 is HTTP-only (no headless browser), we do the best we can from the HTML:

Fetch homepage HTML.
Look for a <script type="application/mcp+json"> tag.
Look for <meta name="mcp-webmcp" content="..."> hints.
Look for any /.well-known/webmcp.json convention file.

In V2 (headless browser), we'll evaluate window.mcp live.

Pass Warn Fail Matrix

Condition	Status	Score
HTML declares a WebMCP block with ≥1 tool	pass	1.0
Only a `meta` or `.well-known/webmcp.json` hint present	warn	0.6
Nothing detected	fail	0.0

Weight is only 1 — WebMCP is early.

Remediation Prompt

If your site is client-interactive and could expose in-page agent tools, publish a WebMCP descriptor in the HTML:

    <script type="application/mcp+json">
    {
      "version": "1.0",
      "tools": [
        {
          "name": "add_to_cart",
          "description": "Add the currently viewed product to the user's cart.",
          "inputSchema": { "type":"object","properties":{"productId":{"type":"string"}},"required":["productId"] }
        }
      ]
    }
    </script>

Implement the corresponding handler on window.mcp.
Only expose tools that act within the user's current authenticated context.

References

Test Fixtures

pass-script-tag.html
warn-meta-only.html
fail-none.html

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