@deepfirstsearch/agent-pay-langchain

@deepfirstsearch/agent-pay-langchain

A LangChain.js tool, ready for LangGraph (ToolNode, createReactAgent), that lets an agent fetch x402 APIs and pay them in USDC on Base while an owner-signed, on-chain budget decides every payment. A prompt-injected agent can ask for any URL; it can't pick the payee, the price or the limit.

Beta, unaudited. Use Base Sepolia or small amounts on Base mainnet.

npm install @deepfirstsearch/agent-pay-langchain @deepfirstsearch/agent-pay @langchain/core @langchain/langgraph

import { createReactAgent } from "@langchain/langgraph/prebuilt";
import { createAgentPay, MerchantRegistry, burnerPayers, vaultFunder } from "@deepfirstsearch/agent-pay";
import { createPaidFetchTool } from "@deepfirstsearch/agent-pay-langchain";

const pay = createAgentPay({
  registry: new MerchantRegistry([
    { origin: "https://api.example.com", payTo: "0x…", network: "eip155:8453", maxPerTx: 50_000n, pricePin: 10_000n },
  ]),
  policy: { allowedNetworks: ["eip155:8453"] },
  payer: burnerPayers(burnerSeed, vault),
  session: { readsUntrustedInput: true, accessesSensitiveData: false, canPay: true },
  ensureFunded: vaultFunder({ agent: agentWallet, publicClient, vault, usdc, intents: { "0x…": intentId }, tranche: 50_000n }),
});

// Seal the plan when the graph starts, before the agent reads anything untrusted.
const plan = pay.commitPlan([{ origin: "https://api.example.com", maxSpend: 200_000n }], 60 * 60_000);

const graph = createReactAgent({ llm, tools: [createPaidFetchTool({ pay, plan })] });
await graph.invoke({ messages: [{ role: "user", content: "Get today's price index from api.example.com" }] });

• The tool's schema is only url, method, body, contentType. Merchants, price pins, caps and the plan live in pay and plan, which the model can't reach.
• It returns a JSON string: { ok: true, status, paid, body } with the body fenced as untrusted data, or { ok: false, refused: true, reason }. Since 0.3.0, with @deepfirstsearch/agent-pay >= 0.8.0, a policy refusal also carries code (stable, e.g. price_changed, payee_mismatch, plan_exhausted) and action (report, ask_owner, fix_config or retry_later); see "Refusal codes" in the SDK README. With older SDKs both are absent.
• Try it offline first: use payer: () => privateKeyToAccount(generatePrivateKey()), drop ensureFunded, and point the registry at startMockServer from @deepfirstsearch/agent-pay/testing (see Test without a chain).
• Create the vault and budgets with the owner CLI.

Develop

npm ci && npm run typecheck && npm test   # includes a LangGraph ToolNode run against a mock x402 merchant