WebMCP TypeScript API

[Alex McManus]

Are there official TypeScript types and docs for the WebMCP API, as implemented in the Chrome preview?

I've been looking at `@mcp-b/webmcp-types` (https://github.com/WebMCP-org/npm-packages/tree/main/packages/webmcp-types), but it doesn't look like your `react-flightsearch` demo complies with those type definitions.

In particular, where you define an `outputSchema`, your `execute` function returns a matching value directly. Whereas in `@mcp-b/webmcp-types`, it expects the `execute` function to return an envelope around the response with `content` and `structuredContent` properties, where `structuredContent` matches the output schema. This seems to align with the original MCP API for tools.

Is this an error in your demo, or are you working to a different version of the API?

Thanks, Alex.

[Alex Nahas]

Hi Alex,

Maintainer of the @mcp-b/webmcp-types package here.

To answer directly: the demo is correct. The @mcp-b/webmcp-types package is stricter than the spec requires, the W3C WebMCP IDL defines ToolExecuteCallback as returning Promise<any>, not CallToolResult.

You're also right that outputSchema is on track to be in the spec, but for now neither input nor output schemas are validated; they exist only as semantic hints (tracked in webmachinelearning/webmcp#92).

I've opened an issue to make the types more permissive and align with the actual IDL. Any thoughts on the proposed changes are welcome.

Cheers,
Alex

[Alex McManus]

Appreciate your help, thanks very much!

Alex

[François Beaufort]

FYI I've just filed an issue to track hosting official TypeScript types for WebMCP: https://github.com/webmachinelearning/webmcp/issues/190

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