WebMCP Documentation

A site’s valid actions change with route, selected record, permissions, and workflow state. The published tool set should change with them. Agents should see only actions that are currently meaningful and authorized, with descriptions and schemas that match the active application context. The current registration pattern ties a tool to an AbortSignal:

Registration lifetime

const controller = new AbortController();
await document.modelContext.registerTool(tool, { signal: controller.signal });

// Remove the registration during route or component cleanup.
controller.abort();

Duplicate names reject instead of replacing the existing tool. When a route, description, schema, or permission boundary changes, abort the old registration before publishing the replacement:

Replace a registration

controller.abort();

const nextController = new AbortController();
await document.modelContext.registerTool(nextTool, {
  signal: nextController.signal,
});

The document remains the owner of this lifecycle. Callers do not retain a separate runtime or server handle. The toolchange event lets consumers refresh their catalog after registration or cleanup. See Build your first React tool and the WebMCP standard API.

Explanation

Architecture

Trust and status

Tool lifecycle and dynamic registration