Give your model Agentcard's instructions

Put appInstructions() at the start of your model’s system prompt. Your model then describes what Agentcard can do in Agentcard’s own words, and sends every shopping request to the buy tool.

agent.ts

import { appInstructions } from '@agent-cards/commerce-sdk';

const system = appInstructions({ markdown: true });

Pass the instructions to your model

Use the string as your system prompt, with the buy tool beside it. buy is the tool you build for the shopper, as the quickstart shows. Its sendLink hands your app each link: a step the shopper opens, such as the one to add a card, and each product or store card, where a flight option carries no URL. Sending each link shows every kind:

agent.ts

import Anthropic from '@anthropic-ai/sdk';
import { appInstructions, buyTool } from '@agent-cards/commerce-sdk';

const buy = buyTool({
  agentcard,
  externalUserId: shopper.id,
  sendLink: (link) =>
    ['vault', 'approval', 'store_login'].includes(link.kind)
      ? sendStep(shopper.id, link) // your code: a step the shopper opens
      : sendCard(shopper.id, link), // your code: a product or store card
});

const answer = await new Anthropic().beta.messages.toolRunner({
  model: 'claude-sonnet-5-5',
  max_tokens: 16000,
  system: appInstructions({ markdown: true }),
  tools: [buy],
  messages,
});

The buy tool’s own description tells the model how to call the tool and what each answer means. appInstructions() tells the model what Agentcard can do for the shopper and how to write.

Say how your app shows text

Pass markdown: true when your app shows the model’s words as Markdown. A shopper who asks for a table then gets a table. Leave it out when your app shows plain text, such as an SMS chat: the model writes no Markdown and starts each list line with • . Pass textingStyle: true when your app is a chat that writes in lowercase, the way a person texts. Pass the same value you pass to buyTool, so the model’s words and Agentcard’s read alike.

agent.ts

const system = appInstructions({ markdown: false, textingStyle: true });

Add your own lines

Write your own lines after Agentcard’s, and keep them about your app, such as its name or the current date.

agent.ts

const system = [
  appInstructions({ markdown: true }),
  'You are the shopping assistant in Acme. Each message opens with the shopper\'s local time.',
].join('\n\n');

Leave out lines about which stores Agentcard reaches or how to format a reply. appInstructions() covers both, and its text changes with each SDK release. A line of your own that says “no markdown” or “most online stores” contradicts Agentcard’s instructions. The shopper then reads two different answers in one chat.

See what your model reads

Print the string to read it. The block below shows the first lines of a call with markdown: true and textingStyle: true.

You help a shopper buy what they ask for, with the `buy` tool from Agentcard.

When the shopper asks what you can do, answer from these lines without calling the tool:

The text ships inside the package, so your app makes no request to read it. APP_INSTRUCTIONS_VERSION names the version of the text you run. Log it with each conversation to know which instructions your model had.

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Give your model Agentcard's instructions

Pass the instructions to your model

Say how your app shows text

Add your own lines

See what your model reads

​Pass the instructions to your model

​Say how your app shows text

​Add your own lines

​See what your model reads

Pass the instructions to your model

Say how your app shows text

Add your own lines

See what your model reads