Agent SDK — Quickstart

Let your AI agent pay L402-protected APIs automatically. Blink or Alby wallet, budget control, MCP and LangChain ready.

What this does

l402-kit ships a built-in client that lets any AI agent — or any script — call L402-protected APIs without writing the payment loop yourself.

Agent  →  GET /api/data
API    →  402 + BOLT11 invoice
Agent  →  pay invoice (Blink / Alby)
Agent  →  GET /api/data  Authorization: L402 macaroon:preimage
API    →  200 ✓

Everything in between — invoice parsing, wallet call, retry — is handled automatically.

---

Node.js / TypeScript

1. Install

npm install l402-kit

2. Pick a wallet

Blink

Get credentials at dashboard.blink.sv → API Keys.

import { L402Client, BlinkWallet } from "l402-kit";

const client = new L402Client({
  wallet: new BlinkWallet(
    process.env.BLINK_API_KEY!,
    process.env.BLINK_WALLET_ID!,
  ),
  budgetSats: 1000, // max spend per session
});

const res = await client.fetch("https://api.example.com/premium");
const data = await res.json();
console.log(data);

Alby

Get your access token at getalby.com → Settings → Access Tokens.

import { L402Client, AlbyWallet } from "l402-kit";

const client = new L402Client({
  wallet: new AlbyWallet(process.env.ALBY_TOKEN!),
  budgetSats: 1000,
});

const res = await client.fetch("https://api.example.com/premium");
const data = await res.json();
console.log(data);

---

Python

1. Install

pip install l402kit

2. Call the API

Blink

import os
from l402kit import L402Client
from l402kit.wallets import BlinkWallet

client = L402Client(
    wallet=BlinkWallet(os.environ["BLINK_API_KEY"], os.environ["BLINK_WALLET_ID"]),
    budget_sats=1000,
    on_spend=lambda sats, url: print(f"Paid {sats} sats → {url}"),
)

r = client.get("https://api.example.com/premium")
print(r.json())

Alby

import os
from l402kit import L402Client
from l402kit.wallets import AlbyWallet

client = L402Client(
    wallet=AlbyWallet(os.environ["ALBY_TOKEN"]),
    budget_sats=1000,
)

r = client.get("https://api.example.com/premium")
print(r.json())

---

What happens step by step

1. client.fetch / client.get sends the request without any auth header
2. If the API returns 402, the client reads the invoice and macaroon from the response body (or WWW-Authenticate header)
3. It checks your budget — throws BudgetExceededError if the price would exceed the limit
4. It calls wallet.payInvoice(bolt11) and waits for the preimage
5. It retries the request with Authorization: L402 <macaroon>:<preimage>
6. Returns the final Response/httpx.Response to your code

No 402? The response is passed through untouched.

---

Spending report

// TypeScript
const report = client.spendingReport();
// { total: 42, remaining: 958, byDomain: { "api.example.com": 42 }, transactions: [...] }

# Python
report = client.spending_report()
print(f"Spent {report.total} sats, {report.remaining} remaining")

---

Next steps

Wallets

Blink, Alby — full setup and options

Budget control

Per-domain limits, callbacks, reports

MCP Server

Claude Desktop integration in 2 minutes

LangChain

Drop-in tool for LangChain agents