Contact emails
[email protected], [email protected], [email protected], 
[email protected], [email protected], [email protected]


Explainer
https://github.com/webmachinelearning/webmcp


Specification
https://webmachinelearning.github.io/webmcp


Design docs

https://docs.google.com/document/d/1ZaQvuj4YnUnoqOfEhbfgFynpDRKk2zZZHavTNJ151gM/edit?tab=t.0#heading=h.ggi78l861caa
https://docs.google.com/document/d/1ycdzuXA-VE8lRDFSArh0Um3PChHV0Hq6Om1MSMG8qPE/edit?tab=t.0#heading=h.edohi3f5z12h


Summary
WebMCP is a proposal for a web API that enables web pages to provide 
agent-specific paths in their UI. With WebMCP, agent-service interaction takes 
place via app-controlled UI, providing a shared context available to app, 
agent, and user.


Blink component
Blink>Agentic Platform>WebMCP


Web Feature ID
navigator.modelContext (WebMCP)


Search tags
WebMCP


TAG review
Spec is being incubated. We will request TAG review before shipping.


TAG review status
Pending


Goals for experimentation
For the experiment we are focused on understanding the API ergonomics for 
agentic workflows across various verticals such as web commerce and 
productivity. We expect the site owners to implement WebMCP tools in their 
sites to automate high-value workflows for them and will seek feedback on the 
functionality of WebMCP. We also plan to gather metrics for tool usage and 
latency, and assess opportunities for improvements.


Origin Trial documentation link
https://docs.google.com/document/d/1ZaQvuj4YnUnoqOfEhbfgFynpDRKk2zZZHavTNJ151gM/edit?tab=t.0#heading=h.ggi78l861caa


Risks




Interoperability and Compatibility
Given this is a new space and new API - there's no compatibility risk. Usual 
risk related to other browser vendors not adopting the API apply. This API is 
meant to augment capabilities provided by browser add-ons and so non-adoption 
in other engines would have limited user-impact and thus we consider the risk 
to be low.

Gecko: No signal

WebKit: No signal

Web developers: No signals Web Framework developers: Have shown a great deal of 
interest during the developer trial, as evidenced here: 
https://www.star-history.com/?repos=webmachinelearning%2Fwebmcp&type=date&legend=bottom-right
 Chrome web store features about 9 different extensions with WebMCP on their 
title and 4* or more ratings. 
https://chromewebstore.google.com/search/WebMCP?minimalRating=4

Other signals:


Ergonomics
There is a risk that site authors that wish to incorporate WebMCP tools into 
their sites will need to duplicate functionality that currently exists to drive 
the user interface. We're hoping that most imperative WebMCP tools are just 
thin wrappers around existing code that drives actions on the site, but we are 
working with framework developers like React to ensure that WebMCP tools can be 
added without rearchitecting the site logic. We are also offering a declarative 
version that requires only adding attributes to existing form elements, which 
is much lighter weight to deploy and does not require any refactoring of 
existing site functionality.


Activation
There are no activation requirements to register WebMCP tools. To execute 
WebMCP tools does require an agent, either provided by the browser or site 
author, to formulate and orchestrate tool calls. There are several Chrome 
extensions already available that allow cloud-LLM-based agents to discover and 
call WebMCP tools. It is also possible to use the Prompt API to call WebMCP 
tools using on-device models.


Security
Sites may consume and expose sensitive information when their WebMCP tools are 
called by agents. Agents should implement safeguards to ensure that sensitive 
information is passed to sites and between origins only under the consent of 
the user that is supervising them. LLM-based agents are susceptible to attacks 
such as indirect prompt injection, which can cause an exploited agent to 
exfiltrate sensitive information in its context to an attacker. Agents should 
implement safeguards against prompt injection and related attacks.


WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it 
has potentially high risk for Android WebView-based applications?
No information provided



Ongoing technical constraints
No technical constraints for the experiments.


Debuggability
Explicit debugging support through a new WebMCP Chrome DevTools Protocol 
domain. The domain supports listing registered tools, invoking tools, and 
logging all calls by agents. Registration issues for declarative tools (eg, 
missing names or descriptions) are reported through the Audits domain.


Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, 
ChromeOS, Android, and Android WebView)?
Yes


Is this feature fully tested by web-platform-tests?
No
The IDL and basic usage is tested via WPTs. Since the API provides the user 
agent with the ability to call certain tools, we might need to extend the WPT 
harness to support this.


DevTrial instructions
https://docs.google.com/document/d/1rtU1fRPS0bMqd9abMG_hc6K9OAI6soUy3Kh00toAgyk/edit?tab=t.0


Flag name on about://flags
Experimental Web Platform features


Finch feature name
WebMCP


Requires code in //chrome?
True


Tracking bug
https://crbug.com/445637567


Launch bug
https://launch.corp.google.com/launch/4460611


Estimated milestones


Shipping on desktop 157

Origin trial desktop first 149

Origin trial desktop last 156

DevTrial on desktop 146

Shipping on Android 157

Origin trial Android first 149

Origin trial Android last 156

DevTrial on Android 146

Shipping on WebView 157

Origin trial WebView first 149

Origin trial WebView last 156




Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/5117755740913664?gate=6226783774703616


Links to previous Intent discussions
Intent to Prototype: 
https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CANMmsAtRdyRw1WtO5va0K%3D_adYH-FRh01xvw5%2BosSd_DAq%3D%3DUQ%40mail.gmail.com
Ready for Trial: 
https://groups.google.com/a/chromium.org/g/blink-dev/c/bhhOmTGzD5Y/m/PGdM8lF6AQAJ



This intent message was generated by Chrome Platform Status.

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