WebMCP declarative API

Declarative WebMCP maps annotated HTML forms to tools while keeping the form visible to the user. Its proposal and implementation details remain split across upstream sources.

Upstream sources

Need	Source
Current proposal design	Declarative API explainer
Proposal integration status	Declarative section of the Community Group draft
Chrome attributes, events, and submission behavior	Chrome declarative API
Executable compatibility cases	Declarative Web Platform Tests
Tool and form design guidance	Chrome WebMCP best practices

The Community Group draft does not yet contain a complete normative declarative definition. Treat the explainer as proposal design and Chrome’s documentation as Chrome implementation behavior.

MCP-B coverage

@mcp-b/webmcp-polyfill temporarily adds declarative tools alongside the vendored upstream core until upstream supports them. Existing native SubmitEvent hooks are preserved. @mcp-b/react-webmcp provides JSX declarations for the supported form attributes; it does not add a separate declarative runtime. For imperative JavaScript tools, use the WebMCP API quick reference.

Packages

WebMCP platforms and agents

Core runtime

React

Tooling

Upstream sources

MCP-B coverage

​Upstream sources

​MCP-B coverage

Upstream sources

MCP-B coverage