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WebMCP beta

Emerging standard · detection is a beta, non-scoring signal

WebMCP (Web Model Context Protocol) is a proposed browser standard — championed by Google Chrome, co-developed with Microsoft in the W3C Web Machine Learning Community Group — that lets a website expose structured, callable tools (search, book a table, checkout) directly to an in-browser AI agent, instead of forcing that agent to scrape and guess at the page. AgentFit detects whether a documentation site ships WebMCP and shows it as a beta badge on the audit report.

Why it matters for docs

Server-side MCP connects an agent to external systems. WebMCP is its browser sibling: the tools are ephemeral and tab-bound — they exist only while the user is on the page, run with the live session and DOM, and vanish on navigation. For a docs or API site, supporting WebMCP means an AI agent acting on a user's behalf can actuate the page through a reliable, schema-described contract instead of brittle screen-scraping.

The two ways to adopt it

Declarative API — annotated HTML forms

Add toolname and tooldescription attributes to an ordinary <form> (with optional per-field toolparamdescription / toolparamtitle and a boolean toolautosubmit):

<form toolname="book_table"
      tooldescription="Book a restaurant table"
      toolautosubmit>
  <input name="date" toolparamdescription="Reservation date">
  <button type="submit">Reserve</button>
</form>

Imperative API — JavaScript

navigator.modelContext.registerTool({
  name: 'search_docs',
  description: 'Search the documentation',
  inputSchema: { type: 'object', properties: { q: { type: 'string' } }, required: ['q'] },
  execute: async ({ q }) => { /* ... */ },
});

Browser support

Chrome 149 — origin trial (desktop), since May 2026. Earlier, behind a flag in Chrome Canary 146+.
Edge — expected (Chromium-based; Microsoft co-authors the spec).
Firefox / Safari — no support today.

The origin trial is opt-in per origin — it is not on by default for end users yet. The API is still under active discussion (a March 2026 revision removed the provideContext / clearContext methods), and production adoption is currently near zero. Today, shipping WebMCP is an early agent-ready differentiator rather than a baseline expectation.

How AgentFit detects it (beta)

During an audit we scan the homepage and a sample documentation page for:

Declarative — <form> elements carrying both toolname and tooldescription.
Imperative — navigator.modelContext inside inline <script> elements.
Polyfill — loads of the @mcp-b / webmcp-polyfill packages.

We scan executable markup only — <script> contents and form attributes — never code samples shown inside <pre><code> blocks, so a page that merely documents WebMCP (like this one) is not flagged as implementing it. We do not execute the page's JavaScript or fetch external script bundles, so imperative usage that lives only in an external .js file is not detected. WebMCP detection is a beta signal and does not affect the 0–100 score — see the 26-criteria rubric for what is scored.

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