WebMCP

@ag2b/plugin-webmcp bridges every Tool on the agent into the browser's WebMCP API — so the host browser agent can call the same tools your AG2B agent already uses.

Try it

WebMCP isn't on by default anywhere. To exercise the bridge end-to-end:

1. Open flag settings in Chrome 148.0.7778.56 or higher (currently the only browser shipping WebMCP), enable WebMCP for testing, and restart.
2. Install the Model Context Tool Inspector extension.
3. Generate a Gemini API key at Google AI Studio and paste it into the extension's settings — the inspector needs it to invoke your bridged tools.

Installation

npm i @ag2b/plugin-webmcp

Usage

Install the plugin once, after scopes are registered:

import { createAgent, OpenAiProvider, Scope, Tool } from '@ag2b/core';
import { webmcp } from '@ag2b/plugin-webmcp';
import { z } from 'zod/v4';

const setBackground = new Tool({
  name: 'setBackground',
  description: 'Change the page background color.',
  parameters: z.object({
    color: z.string().describe('Any valid CSS color (name, hex, rgb, etc.)'),
  }),
  handler: ({ color }) => {
    document.body.style.backgroundColor = color;
  },
});

const agent = createAgent({ provider: new OpenAiProvider({ baseURL: '/api/llm' }) });
agent.scopes.register(new Scope({ name: 'appearance', tools: [setBackground] }));

void agent.use(webmcp());

Every tool registered with the agent — now and in the future — appears under navigator.modelContext. Unregister a Scope and its tools disappear from WebMCP too.

What gets bridged

• Tools — name, description, JSON Schema, and execute are mapped 1:1. Tool name validation, Zod validation, and enabled checks all run inside the bridged execute callback, so disabled tools reject with a descriptive error at call time.
• Scopes — tracked by lifecycle: tools register on onScopeRegister, unregister via AbortController.abort() on onScopeUnregister.
• Scope context — not bridged. WebMCP has no primitive for it.