Plain HTML / vanilla JS

import { registry, startAgentInterface } from "agent-interface-protocol/vanilla";

registry.setState("cart", cart);

registry.registerAction(
  {
    id: "add_to_cart",
    description: "Add a product variant to the cart",
    input_schema: {
      type: "object",
      description: "Variant and quantity",
      properties: {
        variantId: { type: "string", description: "Variant ID from state.catalog" },
        quantity: { type: "string", description: "Whole number as a string" },
      },
      required: ["variantId", "quantity"],
      additionalProperties: false,
    },
    input_example: { variantId: "phone-black-256", quantity: "1" },
    consequential: false,
  },
  ({ variantId, quantity }) => addToCart(variantId, Number(quantity)),
);

const { stop } = startAgentInterface({
  mount: "#agent-panel",      // omit to stay headless
  pages: ["/store"],          // omit to run on every page
  instructions: "Do not place orders without asking.",
});