WebMCP integration

Canonical Client documentation: WebMCP (Client) — configuration, discovery, action formats, and browser notes.

This recipe is a short overview of how the vowel client library works with WebMCP (Web Model Context Protocol) tooling: sharing tools between the browser’s Model Context surface and the voice session. See the W3C Web Machine Learning community draft for the navigator.modelContext API.

What you get

Direction	Behavior
Vowel → WebMCP	Each registerAction tool can be exposed to the browser via navigator.modelContext.registerTool so other on-page Model Context clients can call the same handler.
WebMCP → Vowel	Optional discovery of tools already registered in the page (testing API or a global registry) and registration as Vowel actions so the voice model can call them.

Configuration is on the Vowel client via webMCP in your client config. See WebMCP (Client) for the full feature set.

Configuration

import { Vowel } from '@vowel.to/client';

const vowel = new Vowel({
  apiKey: 'vkey_...',
  // ... other config
  webMCP: {
    /** Discover third-party / page-registered WebMCP tools and register them as Vowel actions */
    enableDiscovery: true,
    /** Expose each Vowel action to WebMCP (default: true) */
    enableExposure: true,
  },
});

• enableExposure (default true) — When the native API is available, Vowel registers each of your actions with the browser’s tool registry so non-voice Model Context clients can execute the same functions.
• enableDiscovery (default false) — When true, the client looks for tools exposed via the WebMCP testing API (navigator.modelContextTesting.getTools) or, as a fallback, the page-level window.__webmcp_tools array used by some hosts, and registers them as Vowel actions before the session uses them.

Manual rediscovery

If tools appear after first load (dynamic imports, client-side registration), call:

await vowel.rediscoverWebMCPTools();

Discovery must remain enabled in config (webMCP.enableDiscovery: true).

Action shape: legacy vs WebMCP

The client accepts legacy parameter-style actions and WebMCP-style actions that use a JSON Schema-style inputSchema. You can use isLegacyAction from @vowel.to/client to narrow definitions; WebMCP-style actions include name and inputSchema. For WebMCP-style definitions, the client converts schemas when registering tools with the browser. See WebMCP (Client) for detail.

Browser support

• Native navigator.modelContext / registerTool is experimental and may require a Chromium build with the Model Context / WebMCP feature enabled.
• If the native API is missing, exposure may be limited; discovery can still use the testing API or __webmcp_tools where your host provides them.
• For current behavior and logs, use the client debug log level and watch [webmcp] / [VowelClient] console lines at startup and when registering actions.

See also

• Custom actions — Registering tools before startSession().
• Connection paradigms — Token and session setup.

Changelog

Client releases note WebMCP in @vowel.to/client CHANGELOG under Unreleased / version sections.