draft community group report · S-074
WebMCP
Let websites expose structured tools to compatible user agents.
Markdown · JSON · Canonical source
- Revision
- 2026-08-26 draft
- Maturity
- draft community group report
- Authority
- W3C Web Machine Learning Community Group
- Structure
- Web API and HTML/JavaScript tool exposure with web-platform tests
- Roles
- website, user-agent, agent
WebMCP sits at the website-to-agent boundary. It is not the same thing as configuring a remote MCP server, even when product language uses similar “tools” terminology.
The research snapshot records a draft Community Group Report. Any positive implementation assertion should name the draft revision, runtime or browser version, flags, origin/security conditions, and evidence class.
Catalog mapping
Atomic capability rows
Absence here means the feature tree has not yet been published, not that the specification lacks the capability.
- WebMCPExpose website functionality as structured tools through a browser-mediated agent boundary.
- WebMCP declarative form toolsExpose semantic HTML forms as structured tools through WebMCP annotations.
- WebMCP execution cancellationCancel pending tool registration or execution through abort signals and lifecycle rules.
- WebMCP imperative toolsRegister JavaScript-backed tools through document.modelContext.registerTool().
- WebMCP permissions policyGate tool exposure across documents and origins through the tools permissions policy.
- WebMCP security annotationsCommunicate read-only and untrusted-content hints across the site-to-agent boundary.
- WebMCP tool discoveryExpose the active page tool list and schemas to a WebMCP-aware agent.
- WebMCP tool executionInvoke a page tool with structured arguments and return its result to the agent.
Conformance boundary
Proposed tests
Definitions only. No fixture has been executed against a harness.
- T-WEB-001navigator.modelContext tool registration · draft