WebMCP Documentation

The authoritative API definition is the W3C WebMCP specification. Chrome’s current implementation notes live in the Chrome WebMCP imperative API docs.

Canonical surface

New code uses document.modelContext.

Member	Purpose
`registerTool(tool, { signal })`	Publish a tool and bind its lifetime to an optional abort signal
`getTools()`	Discover registered tool objects
`executeTool(tool, inputJson, options?)`	Execute a tool object returned by `getTools()`
`toolchange`	Notify consumers that available tools changed

const controller = new AbortController();

document.modelContext.registerTool(tool, {
  signal: controller.signal,
});

controller.abort();

getTools() and executeTool() are the producer-facing discovery and execution path in Chrome’s current preview. registerTool() returns Promise<void>, and tool cleanup is tied to the optional AbortSignal passed at registration time.

Compatibility

navigator.modelContext is a deprecated alias for migration.
navigator.modelContextTesting is a compatibility surface for testing.
listTools(), deprecated callTool() compatibility helpers, prompts, resources, sampling, elicitation, and transports are MCP-B extensions.
outputSchema is not part of the current W3C/Chrome WebMCP tool dictionary. MCP-B packages expose it as helper metadata for type inference, structured MCP responses, and polyfill/runtime adapters.

See @mcp-b/webmcp-polyfill for the portable strict runtime.

Packages

WebMCP standard

Core runtime

React

Tooling

WebMCP standard API

Canonical surface

Compatibility

​Canonical surface

​Compatibility

Canonical surface

Compatibility