Reference

WebMCP

A browser page may expose tools for its current visible context. Execution calls the same endpoint as the human action, with origin checks and session policy.

Example tools

search_current_campaigns
open_decision_trace
prepare_budget_change
preview_warrant_request

javascriptfeature detection

if (document.modelContext?.registerTool) {
  document.modelContext.registerTool({
    name: "prepare_budget_change",
    description: "Draft a budget change. Requires human approval.",
    inputSchema: { type: "object",
      properties: { campaignId: { type: "string" },
                    deltaMicros: { type: "integer" } } },
    execute: ({ campaignId, deltaMicros }) =>
      fetch("/v1/budget-changes/preview", {
        method: "POST", headers: { "Content-Type": "application/json" },
        body: JSON.stringify({ campaignId, deltaMicros })
      })
  });
}

No one-step money. High-risk actions cannot be completed from a browser tool alone. The agent prepares; the server checks an immutable approval package.