The site declares what it can do
The agent does not have to guess at buttons. The site names each tool, what it takes and what it returns.
WebMCP client
Call
the
tools
a
website
registers
for
AI
agents,
through
WebMCP
WebMCP lets a website register tools for agents, such as add to cart, search flights or file a ticket. Browsentic detects them, gives your agent their schemas, and calls them through the site’s own code.
The standard
What WebMCP is
WebMCP is a W3C proposal shipping natively in Chrome: a page registers tools on document.modelContext, each with a name, a description, an input schema and a handler the site wrote.
The site’s code does the work
A registered handler runs the same logic the UI runs, so a call cannot miss a selector or catch the page mid-render.
One call instead of a click sequence
Add to cart becomes one schema-checked call instead of find, scroll, click, wait and verify.
How Browsentic uses it
How Browsentic finds and calls site tools
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01
The snapshot lists them
The page snapshot carries a siteTools list whenever a page registers any, so the agent knows the site has tools.
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02
The agent reads the schemas
page_listSiteTools returns every tool the site registered: name, description and input schema, ready to call.
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03
The site runs the call
page_callSiteTool runs one by name, through the site’s own handler, and returns whatever it produced.
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04
You approve it first
A site tool call is gated like a form submit, because the site decides what it does. It pauses in the panel and says which tool it will call.
Coverage
Which implementations it finds
It reads from the page’s main world, so it finds whichever implementation the site uses.
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document.modelContext, native in Chromeanswers -
navigator.modelContext, the older aliasanswers -
Library and polyfill implementationsanswers -
Sites that register nothingordinary tools
The last row is most of the web today. There the ordinary page tools do the job, and the agent is told not to look for site tools.
Safety
Site tool calls follow the approval rules
Calls are gated like submits
The site-tool-call rule pauses every call in the side panel first, because the site decides what a tool does.
Listing is read-only
Discovering tools and reading schemas changes nothing on the page, so autonomous site maps record which pages are agent-ready without acting on them.
No debugger needed
Reading a page’s registered tools uses the extension’s ordinary scripting permission. Nothing is injected for you to approve, and no debugger bar appears.
MCP clients are denied by default
An MCP client has nobody to answer a prompt, so its calls follow the unattended policy, which denies them until you change it.
Keep reading
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