WebMCP Documentation

The declarative proposal turns annotated HTML forms into agent-readable tools while preserving browser validation and user review. The Community Group draft’s declarative section is still an explicit TODO, so Chrome’s current implementation defines the practical compatibility target.

Agent-readable search form

<form toolname="search_catalog" tooldescription="Search the product catalog">
  <label>
    Query
    <input name="query" toolparamdescription="Words to match in the catalog" required />
  </label>
  <button type="submit">Search</button>
</form>

Surface	Behavior
Form without `toolautosubmit`	The browser fills the form and waits for the user to submit it
Form with `toolautosubmit`	The browser submits the form when the agent invokes the tool
`SubmitEvent.agentInvoked`	Reports whether an agent initiated the submission
`SubmitEvent.respondWith(promise)`	Associates the resolved value with the tool call after the handler calls `preventDefault()`
`toolactivated` and `toolcancel` events	Report when an agent operation is activated or canceled

The attribute names, schema synthesis rules, constraint mapping, submission behavior, and iframe model are still evolving. Use Chrome’s Declarative API docs for current browser behavior. Track the Community Group declarative draft section and declarative explainer for proposal status. Do not treat this example as a stable compatibility contract. @mcp-b/webmcp-polyfill implements the tested local-document subset and documents its native-only gaps. React users can write these attributes directly after importing @mcp-b/react-webmcp. For imperative JavaScript registration, use document.modelContext.registerTool().

Packages

WebMCP standard

Core runtime

React

Tooling

WebMCP declarative API