Skip to main content
WebMCP (Web Model Context) is an early W3C Web Machine Learning proposal that lets a page register JavaScript tools an AI agent operating in the user’s browser can discover and call. Chrome ships it behind a flag as navigator.modelContext, and ChatGPT Atlas implements it as “site tools”. The Laso Finance web app registers a WebMCP toolset on every page load. There is nothing to install and no credential to configure: the tools run inside the page and act as the user who is signed in to that browser tab.
WebMCP is for agents that live in the user’s browser. Agents running anywhere else should use the x402 HTTP API or the remote MCP server, which expose the full product surface with their own authentication and payment rails.

​
Requirements

  • A browser with WebMCP support: Chrome 146+ with the WebMCP flag enabled in chrome://flags, or ChatGPT Atlas.
  • The user signed in at laso.finance for any tool that reads or moves their money. The read-only site tools work logged out.
Feature detection is silent: in a browser without the API the page registers nothing and behaves normally.

​
The tools

Read state: Navigate and hand off to the human: Act as the logged-in user: Products without a write tool (international cards, gift cards, Venmo/PayPal, push-to-card) are reachable through open_page: the agent navigates, the human completes the order form.

​
Boundaries

  • Identity verification is human-only. get_identity_verification_status reports state and returns the link; an agent must never fill in a verification flow on the user’s behalf. This mirrors the KYC boundary in the server-side API.
  • Confirm before moving money. The write tools debit the user’s balance immediately. Tool descriptions instruct the agent to confirm amounts with the user first.
  • Deposits are asynchronous. Funds sent to the deposit address credit the balance after on-chain settlement; list_recent_deposits shows what has landed.

​
Relationship to the server-side surface

The WebMCP tools are a convenience layer over the same product. They mirror a subset of what the x402 HTTP API and the remote MCP server expose, minus payments: in the browser there is nothing to pay, because the tools act on the account of the user who is already signed in.