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What is WebMCP?

WebMCP is a Google + Microsoft W3C proposal that lets websites expose callable tools to AI agents. How it works, browser support, and why it matters.

By Ran Erez · Updated 2026-08-28

WebMCP (Web Model Context Protocol) is a proposed web standard that lets a website hand AI agents a set of structured, callable tools — instead of forcing them to screen-scrape the page and simulate clicks. It was jointly proposed by engineers at Microsoft and Google, published as a unified proposal in August 2025, and is now a draft of the W3C Web Machine Learning Community Group.

Agents are already browsing the web (Gemini in Chrome, browser extensions, automation frameworks). Today they operate your site the hard way, by looking at pixels and guessing which button does what. WebMCP lets your page say, in a machine-readable contract, exactly what you can do there and how to do it.

How WebMCP works

A page registers tools through the document.modelContext API (early articles and demos used navigator.modelContext; the getter moved to Document, and Chrome 150+ deprecates the Navigator alias). Each tool has a name, a natural-language description written for the model, a JSON Schema describing its inputs, and an execute callback that runs your existing page JavaScript: 

document.modelContext.registerTool({
  name: "search_products",
  description: "Search the store catalog. Returns product names, prices and URLs.",
  inputSchema: {
    type: "object",
    properties: {
      query: { type: "string", description: "What the user is looking for" },
      maxResults: { type: "number" }
    },
    required: ["query"]
  },
  annotations: { readOnlyHint: true },
  async execute({ query, maxResults = 5 }) {
    const results = await storeSearch(query);
    return results.slice(0, maxResults);
  }
});

When an agent-capable browser visits the page, it discovers the registered tools, reads their schemas, and can invoke them, with the user in the loop and inside the user's existing session. Because the agent acts as the logged-in user, there are no API keys, no OAuth server, and no separate backend integration to build. That is the quiet advantage of running in the page.

There is also a declarative path. Annotate a standard HTML form with tool attributes and the form itself becomes an agent tool with zero JavaScript. Chrome's "Le Petit Bistro" demo exposes a restaurant reservation form to agents this way.

Browser support in 2026

WebMCP is not the same as MCP

Anthropic's Model Context Protocol (MCP) connects AI assistants to backend servers, out-of-band from your website. WebMCP runs inside the page, in the user's browser and session. They're complementary layers of the same "agentic web" stack — we break the whole stack down in WebMCP vs MCP vs llms.txt.

Why it matters for your business

Early research on the browser-tab-as-tool-server approach reports agents completing tasks with dramatically fewer tokens and higher success rates than pixel-based actuation (one 2025 paper measured a 67.6% token reduction and ~98% task success on tool-based flows). Meanwhile Cloudflare scanned 200,000 sites for agent readiness — only about 4% passed its content-accessibility check (Cloudflare). At Google I/O 2026, Google named Expedia, Booking.com, Shopify, Etsy, and Target among the brands already experimenting with WebMCP (via Search Engine Journal); Shopify has since shipped it natively on every storefront. The gap between agent-ready sites and everyone else matters because when an agent can't use your site, it completes the task on a competitor's.

Which tools should your site expose? That depends on your business type — we maintain a cookbook of WebMCP tool patterns by industry, and our deep audit produces a blueprint specific to your site.

Sources and further reading