mcp-handler now has experimental support for WebMCP, the proposed web standard for exposing tools to in-browser agents. Add a single script tag to your site, and your existing MCP tools become available there too.

Opt tools in by adding them to the experimental_webMcp object:

import { createMcpHandler } from "mcp-handler";
const handler = createMcpHandler(
  (server) => {
    server.registerTool("roll_dice", /* ... */);
  },
  {
    experimental_webMcp: {
      tools: ["roll_dice"],
    },
  },
);
export { handler as GET, handler as POST };

Then load the script from your MCP endpoint with the ?webmcp-script parameter:

<script src="/api/mcp?webmcp-script"></script>

The script registers those tools with the page and proxies each call back to your MCP server as the signed-in user, so authenticated tools work without a browser-side OAuth flow.

Upgrade to [email protected] and read the documentation to get started.