WebMCP Agency
Check a site

Status

WebMCP in Chrome: status, flag and tools

Updated · Checked against the WebMCP draft of 20 October 2026 · By the Convertlyft research team

On this page
  1. Which browsers support WebMCP?
  2. How do I turn on WebMCP in Chrome?
  3. How Chrome behaves in practice
  4. Chrome version notes
  5. The WebMCP inspector in DevTools
  6. Lighthouse WebMCP audits
  7. Is there a WebMCP extension?
  8. Checking your own site
  9. Page history

As of 24 October 2026, WebMCP in Chrome has been a DevTrial since Chrome 146. An origin trial runs from Chrome 149 to Chrome 156 inclusive, and shipping is planned for Chrome 157. Developers can turn it on locally with the flag chrome://flags/#enable-webmcp-testing.

This page covers browser support, how to switch WebMCP on, and the Chrome tools for testing it. If you are new to WebMCP, start with what is WebMCP.

Which browsers support WebMCP?

Chrome and Microsoft Edge run WebMCP origin trials; Mozilla’s position on WebMCP is “neutral” and WebKit’s is “oppose”.

Browser support as of 24 October 2026.

Browser or agent Status
Chrome DevTrial from Chrome 146 (desktop and Android). Origin trial from Chrome 149 to 156 inclusive (desktop, Android, WebView). Shipping planned for Chrome 157.
Microsoft Edge Origin trial live in Edge 150, per the WebMCP repository’s status page. Microsoft’s trial page lists expiry on 30 March 2027.
Firefox Mozilla’s standards position is “neutral”. A refreshed position was pending as of 9 October 2026.
Safari WebKit’s standards position is “oppose”.
Brave Experimental support in Leo AI chat.
ChatGPT Desktop Listed as supported.
Meta Ray-Ban Display “Coming soon” for Web Apps; off by default and enabled per device.

The Chrome plan comes from Google’s “Intent to Experiment” post on the blink-dev mailing list, posted on 15 May 2026 and approved on 18 May 2026. Calendar dates for Chrome 156 and 157 are not stated there.

Google, Gemini and WebMCP

At Google I/O on 19 May 2026, Google announced the origin trial in Chrome 149. It also said Gemini in Chrome “will soon support WebMCP APIs”. We have found no confirmation from Google that this has shipped.

Microsoft Edge

Microsoft co-edits the spec. Two of the four spec editors work at Microsoft, alongside two at Google. Edge runs its own WebMCP origin trial, which Microsoft lists as expiring on 30 March 2027.

How do I turn on WebMCP in Chrome?

To turn on WebMCP in Chrome for local testing, open chrome://flags/#enable-webmcp-testing, set it to Enabled and restart Chrome. For real visitors, register your origin for the “WebMCP” origin trial, which runs from Chrome 149 to 156.

For local testing: the flag

  1. Open chrome://flags/#enable-webmcp-testing in Chrome.
  2. Set it to Enabled.
  3. Restart Chrome.

This only changes your own browser. Visitors to your site are not affected.

For real visitors: the origin trial

An origin trial lets a site turn on an experimental feature for its visitors for a limited time, without them changing any settings.

  1. Register your origin for the trial named “WebMCP” on the Chrome origin trial signup page.
  2. Add the trial token you receive to your pages, as described in Chrome’s origin trial blog post.
  3. Keep your feature check in place, because the trial ends after Chrome 156.
if (document.modelContext?.registerTool) {
  // WebMCP is available: register your tools here.
}

Always use document.modelContext. Older posts use navigator.modelContext, which the spec replaced on 19 May 2026.

The early preview

Before the origin trial, Chrome ran an early preview. Its blog post “WebMCP is available for early preview” was published on 10 February 2026. Chrome’s WebMCP docs hub followed on 18 May 2026.

Turning WebMCP off for a page

WebMCP is controlled by a Permissions Policy feature called "tools". By default it is allowed for the page’s own origin ('self'). To switch it off, send this response header:

Permissions-Policy: tools=()

A cross-origin iframe (a frame from another site embedded in your page) gets WebMCP only if you allow it:

<iframe src="https://widget.example" allow="tools"></iframe>

If the policy blocks WebMCP, registerTool() rejects with NotAllowedError.

How Chrome behaves in practice

Chrome’s docs add a few practical details:

  • getTools() returns tools in alphabetical order.
  • executeTool() returns null when the call triggers a navigation.
  • Tools are hidden from other origins unless the page lists the caller’s origin in exposedTo and the caller names this origin in fromOrigins. Chrome’s security guidance says: “Only expose your tools to origins that you trust”.

Chrome version notes

Some behaviour depends on the Chrome version:

Chrome version Change
146 DevTrial starts
149 Origin trial starts
150 Needed for the Lighthouse “Agentic browsing” category
153 Removing a tool no longer cancels calls to it that are already running
155 Passing JSON-stringified input to executeTool() is deprecated; pass an object
156 window.ontoolactivated and window.ontoolcancel no longer work; listen on document.modelContext. The debugging annotation is available. Last origin trial version.
157 Shipping planned

The WebMCP inspector in DevTools

Chrome DevTools has a WebMCP pane in the Application panel. It does three things:

  • Lists the tools the page has registered, with how many times each was called.
  • Logs each call with its input and output.
  • Lets you run a tool by hand.

This is the quickest way to see whether your tools registered and whether an agent would see the names and descriptions you expect.

For coding agents: Chrome DevTools MCP

Chrome DevTools for agents (chrome-devtools-mcp) has two WebMCP tools, list_webmcp_tools and execute_webmcp_tool. They sit behind the --categoryExperimentalWebmcp flag.

Chrome’s “Modern Web Guidance” also includes a webmcp skill for coding agents.

The DevTools Protocol

The Chrome DevTools Protocol (CDP) has an experimental WebMCP domain. It includes the commands enable, disable, invokeTool and cancelInvocation, and the events toolsAdded, toolsRemoved, toolInvoked and toolResponded.

Lighthouse WebMCP audits

Lighthouse added an “Agentic browsing” category in version 13.2.0 (1 May; the release page gives no year) and turned it on by default in 13.3.0 (7 May). The category is informational and has no benchmark score. It needs Chrome 150 or later, and the WebMCP audits need the origin trial.

Audit What it checks
webmcp-registered-tools Lists the page’s tools and warns when more than 40 are registered.
webmcp-schema-validity Flags form tools with tooldescription but no toolname, or the reverse. Also flags required fields without a name.
webmcp-form-coverage “Forms missing declarative WebMCP”: lists forms without both attributes. Informational only.

The 40-tool figure is a Lighthouse warning, not a browser limit. Chrome’s best-practices page says “there isn’t a maximum number of tools allowed”.

Is there a WebMCP extension?

You do not need an extension to use WebMCP in Chrome. The flag or the origin trial is enough. That registers your tools; to call them by hand, use the DevTools WebMCP pane.

Searches for a “WebMCP extension” often lead to community projects. The WebMCP-org project (also known as MCP-B) publishes npm packages, including @mcp-b/webmcp-polyfill. Its installWebMCP() “keeps native support when present”. These are community packages, not Chrome features.

Checking your own site

The DevTools pane shows you one page at a time. To see which pages across your site declare form tools, run the free check. For a fuller look at agent readiness, Convertlyft offers a full WebMCP report.

Ready to build? Read how to add WebMCP. The spec tracker follows changes that affect Chrome’s behaviour.

Page history

  • 24 October 2026: first published; checked against the WebMCP draft of 20 October 2026.

Questions people ask

Which Chrome version supports WebMCP?

As of 24 October 2026, WebMCP has been a DevTrial since Chrome 146. Chrome runs an origin trial from Chrome 149 to Chrome 156 inclusive, and shipping is planned for Chrome 157.

How do I turn on WebMCP in Chrome?

For local development, enable chrome://flags/#enable-webmcp-testing. To turn it on for real visitors, register your origin for the WebMCP origin trial.

Does Microsoft Edge support WebMCP?

As of 24 October 2026, the WebMCP repository's status page lists an origin trial live in Edge 150. Microsoft's origin trial page lists the WebMCP trial as expiring on 30 March 2027.

Is there a WebMCP inspector in Chrome DevTools?

Yes. The Application panel has a WebMCP pane that lists registered tools, logs each call with its input and output, and lets you run a tool by hand.

Sources

  1. Intent to Experiment: WebMCP (blink-dev) (read 2026-10-23)
  2. Chrome for Developers: WebMCP (read 2026-10-23)
  3. Chrome blog: Join the WebMCP origin trial (read 2026-10-23)
  4. Chrome blog: WebMCP is available for early preview (read 2026-10-24)
  5. Chrome at I/O 2026 (read 2026-10-24)
  6. WebMCP implementation status (read 2026-10-23)
  7. Microsoft Edge origin trial: WebMCP (read 2026-10-24)
  8. Mozilla standards position on WebMCP (#1412) (read 2026-10-24)
  9. WebKit standards position on WebMCP (#670) (read 2026-10-24)
  10. Chrome DevTools: WebMCP pane (read 2026-10-23)
  11. Chrome blog: agent-ready toolkit (read 2026-10-23)
  12. Chrome DevTools Protocol: WebMCP domain (read 2026-10-23)
  13. Lighthouse releases (read 2026-10-23)
  14. Lighthouse: Agentic browsing (read 2026-10-23)
  15. Lighthouse audit: registered WebMCP tools (read 2026-10-23)
  16. Lighthouse audit: forms missing declarative WebMCP (read 2026-10-23)
  17. Chrome for Developers: WebMCP best practices (read 2026-10-24)
  18. Chrome for Developers: WebMCP imperative API (read 2026-10-23)
  19. WebMCP-org npm packages (read 2026-10-24)
  20. WebMCP, Draft Community Group Report (20 October 2026) (read 2026-10-23)
  21. Chrome for Developers: Build secure WebMCP tools (read 2026-10-24)