--- title: "WebMCP: what it is | Agent MCP Directory" description: "WebMCP: A browser API that lets a page register JavaScript functions as tools, with descriptions and schemas, that an in-browser agent can call." canonical: https://agentmcpdirectory.com/standards/webmcp site: "Agent MCP Directory" last_updated: 2026-11-04 section: "Standards" --- # WebMCP: what it is | Agent MCP Directory > WebMCP: A browser API that lets a page register JavaScript functions as tools, with descriptions and schemas, that an in-browser agent can call. Source: https://agentmcpdirectory.com/standards/webmcp Site: Agent MCP Directory Last reviewed: 2026-11-04 # WebMCP WebMCP, maintained by W3C Web Machine Learning Community Group (editors from Microsoft and Google). A browser API that lets a page register JavaScript functions as tools, with descriptions and schemas, that an in-browser agent can call. Status: Draft specification; Chrome and Edge test it in an origin trial, Brave behind a flag. ## Fact sheet | Name | WebMCP | | --- | --- | | Maintainer | W3C Web Machine Learning Community Group (editors from Microsoft and Google) | | What it is | A browser API that lets a page register JavaScript functions as tools, with descriptions and schemas, that an in-browser agent can call. | | Status and version | Draft specification; Chrome and Edge test it in an origin trial, Brave behind a flag, no Firefox or Safari implementation (nekuda FAQ, October 2026). | | What it does not do | Does not work without a browser agent that reads the page; does not replace a server-side MCP endpoint; the declarative form-based API is only being explored. | ## Dated facts - The draft documents document.modelContext with registerTool(), getTools(), executeTool() and a toolchange event. ([github.com](https://github.com/webmachinelearning/webmcp), read 4 November 2026) - The imperative registerTool() API is in the spec; a declarative API built from HTML forms is being explored and is not in it. ([github.com](https://github.com/webmachinelearning/webmcp), read 4 November 2026) - WebMCP is on by default in top-level windows and same-origin iframes; cross-origin iframes need the Permissions Policy allow="tools". ([github.com](https://github.com/webmachinelearning/webmcp), read 4 November 2026) - The explainer was first published on 13 Aug 2025; TypeScript definitions ship as the webmcp-types npm package. ([github.com](https://github.com/webmachinelearning/webmcp), dated 13 August 2025, read 4 November 2026) - webmcp.com, maintained by nekuda, reported 8,556 verified sites and 52,491 indexed tools. ([webmcp.com](https://webmcp.com/), read 4 November 2026) - nekuda reports that ChatGPT's desktop app began using WebMCP tools in its built-in browser on 25 Aug 2026. ([webmcp.com](https://webmcp.com/), dated 25 August 2026, read 4 November 2026) - Cloudflare Browser Run moved its WebMCP support to document.modelContext on 28 Sep 2026. ([developers.cloudflare.com](https://developers.cloudflare.com/changelog/post/2026-09-28-webmcp-api/), dated 28 September 2026, read 4 November 2026) - Mintlify ships WebMCP tools such as search\_docs and read\_page on Pro and Enterprise plans. ([www.mintlify.com](https://www.mintlify.com/docs/ai/model-context-protocol), read 4 November 2026) ## Seen in the shared crawl The shared crawl looks for WebMCP in the initial HTML of each home page. It found a WebMCP hint on 25 of 7,545 home pages in the Tranco top 10,000 and on 59 of 3,393 on Ora's leaderboard. ## Compared with - [MCP vs WebMCP](https://agentmcpdirectory.com/compare/mcp-vs-webmcp/) - [WebMCP vs agents.json](https://agentmcpdirectory.com/compare/webmcp-vs-agents-json/) Edition 4 November 2026 Method [How rows are verified](https://agentmcpdirectory.com/method/) Data [CSV and JSON](https://agentmcpdirectory.com/data/) Markdown [This page as markdown](https://agentmcpdirectory.com/standards/webmcp/index.md) ## Sources - [WebMCP specification or home](https://github.com/webmachinelearning/webmcp), read 4 November 2026 - [WebMCP: webmcp.com](https://webmcp.com/), read 4 November 2026 - [WebMCP: developers.cloudflare.com/changelog/post/2026-09-28-webmcp-api](https://developers.cloudflare.com/changelog/post/2026-09-28-webmcp-api/), read 4 November 2026 - [WebMCP: www.mintlify.com/docs/ai/model-context-protocol](https://www.mintlify.com/docs/ai/model-context-protocol), read 4 November 2026 Last reviewed 4 November 2026