Agent frameworks

@tuppence/agent-tools gives an agent framework the same tools as the MCP server — it asks the server for them, with your key — so an agent built with any of them can take payments, and is offered only what its key may do.

npm install @tuppence/agent-tools

Give the agent a restricted key in TUPPENCE_SECRET_KEY, with only the scopes it needs — say payment_links:read and payment_links:write for an agent that sells with links.

OpenAI Agents SDK

import { Agent, run } from "@openai/agents";
import { tuppenceTools } from "@tuppence/agent-tools/openai-agents";

const { tools, close } = await tuppenceTools();
const agent = new Agent({
  name: "Billing assistant",
  instructions: "Amounts are integers in pence. When you create a payment link, reply with its URL.",
  tools,
});
const result = await run(agent, "Make a £15 payment link for a deep research report.");
console.log(result.finalOutput);
await close();

LangChain

import { createAgent } from "langchain";
import { tuppenceTools } from "@tuppence/agent-tools/langchain";

const { tools, close } = await tuppenceTools();
const agent = createAgent({ model: "openai:gpt-5", tools });
const result = await agent.invoke({
  messages: [{ role: "user", content: "Make a £15 payment link for a deep research report." }],
});
await close();

Claude Agent SDK

The Claude Agent SDK connects to MCP servers itself, so the pack is the connection:

import { query } from "@anthropic-ai/claude-agent-sdk";
import { TUPPENCE_TOOLS, tuppenceMcpServer } from "@tuppence/agent-tools/claude-agent-sdk";

for await (const message of query({
  prompt: "Make a £15 payment link for a deep research report.",
  options: {
    mcpServers: { tuppence: tuppenceMcpServer() },
    allowedTools: [TUPPENCE_TOOLS], // or one by one: mcp__tuppence__create_payment_link
  },
})) {
  console.log(message);
}

When the API says no

A refused call is an answer, not a crash: the tool returns the API’s error — code, message, param — for the agent to read and correct. Money-moving tools require an idempotency_key; an agent that retries must send the same one, and the money moves once.

Each example above runs in our CI against the real API, with a scripted model standing in for the LLM: the agent really makes the link, and really gets its URL back.