Pay any endpoint from your agent — 3 chains, no account, no SDK.

HTTP/1.1 402 Payment Required
{"maxAmountRequired": "10000", "payTo": "0xD6E8aF2F65B4C9ACC7BF14A3096056e89E312878"}

// npm i viem — sign once, reuse the token until it expires
import { privateKeyToAccount } from "viem/accounts";
import { randomBytes } from "node:crypto";

const account = privateKeyToAccount(process.env.PRIVATE_KEY);
const recipient = "0xD6E8aF2F65B4C9ACC7BF14A3096056e89E312878"; // Base payTo (always trust the 402 quote)
const value = 1_000_000n;            // 1 USDC ceiling (atomic, 6 decimals)
const validBefore = BigInt(Math.floor(Date.now() / 1000) + 30 * 86400);
const nonce = `0x${randomBytes(32).toString("hex")}`;

const signature = await account.signTypedData({
  domain: { name: "USD Coin", version: "2", chainId: 8453,
            verifyingContract: "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913" },
  types: { TransferWithAuthorization: [
    { name: "from", type: "address" }, { name: "to", type: "address" },
    { name: "value", type: "uint256" }, { name: "validAfter", type: "uint256" },
    { name: "validBefore", type: "uint256" }, { name: "nonce", type: "bytes32" } ] },
  primaryType: "TransferWithAuthorization",
  message: { from: account.address, to: recipient, value,
             validAfter: 0n, validBefore, nonce },
});

const token = Buffer.from(JSON.stringify({
  chain: "base", from: account.address, to: recipient,
  value: `0x${value.toString(16)}`, validAfter: "0x0",
  validBefore: `0x${validBefore.toString(16)}`, nonce, signature,
})).toString("base64url");

console.log(token); // → export TOOLS402_SESSION_TOKEN=<token>

// EVM `exact` — broadcast a USDC transfer yourself, prove it with the txHash.
import { createWalletClient, http, parseAbi } from "viem";
import { privateKeyToAccount } from "viem/accounts";
import { base } from "viem/chains";           // or `polygon`

const ENDPOINT = "https://api.tools402.dev/v1/base64-encode";
const body = JSON.stringify({ data: "hello" });

// 1 · quote
const q = await fetch(ENDPOINT, { method:"POST", headers:{ "Content-Type":"application/json" }, body });
const quote = (await q.json()).accepts.find(a => a.network === "base" && a.scheme === "exact");

// 2 · pay (you pay gas on this chain)
const account = privateKeyToAccount(process.env.PRIVATE_KEY);
const wallet = createWalletClient({ account, chain: base, transport: http() });
const txHash = await wallet.writeContract({
  address: quote.asset,                        // USDC on the chain
  abi: parseAbi(["function transfer(address,uint256) returns (bool)"]),
  functionName: "transfer",
  args: [quote.payTo, BigInt(quote.maxAmountRequired)],
});

// 3 · retry with X-Payment carrying the txHash
const xPayment = Buffer.from(JSON.stringify({
  x402Version: 1, scheme: "exact", network: "base",
  payload: { txHash, from: account.address, to: quote.payTo,
             amount: quote.maxAmountRequired, asset: quote.asset },
})).toString("base64url");
const r = await fetch(ENDPOINT, { method:"POST",
  headers:{ "Content-Type":"application/json", "X-Payment": xPayment }, body });
console.log(await r.json());   // → 200, your result

// npm install @solana/web3.js @solana/spl-token
// Scheme "spl-transfer" — buyer partial-signs; facilitator is fee payer (gasless).

// 1 · ask for 402 — pick accept where network === "solana" from the body
const r402 = await fetch("https://api.tools402.dev/v1/pdf-md", {
  method: "POST",
  body: formData,
});
// → 402 · accepts[0].scheme === "spl-transfer"
// → extra.feePayer === "facilitator" · payTo: Gt9EC4XYqD9pUmTFAfBy9b3gbGG8eiv3ZNLMLCuyU8w8
// → mint EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v (Circle USDC)

// 2 · build TransferChecked tx, partial-sign (buyer only — do NOT broadcast)
const serializedTx = tx.serialize({ requireAllSignatures: false })
  .toString("base64");

// 3 · retry with X-Payment (facilitator co-signs fee payer + broadcasts)
const xPayment = Buffer.from(JSON.stringify({
  x402Version: 1,
  scheme: "spl-transfer",
  network: "solana",
  payload: {
    serializedTx,
    signature: buyerSig,
    from: buyerPubkey,
    to: quote.payTo,
    mint: "EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v",
    amount: quote.maxAmountRequired,
  },
})).toString("base64url");

await fetch("https://api.tools402.dev/v1/pdf-md", {
  method: "POST",
  headers: { "X-Payment": xPayment },
  body: formData,
});
// → 200 OK · facilitator stack (PayAI → Kobaru → local-key-solana) pays gas

// Session token expired or malformed
{ "error": "invalid session token" }

// X-Payment header not valid base64url JSON
{ "error": "X-Payment: invalid base64url JSON" }

// Payload schema mismatch (wrong fields, bad txHash, etc.)
{ "error": "payload: Invalid input" }

# 1 · generate <token> with the Session token snippet above (#session-token · copy-paste, no CLI)

# 2 · add MCP server (Claude Code)
claude mcp add tools402 \
  --command "bunx @tools402/mcp@0.2.2" \
  --env TOOLS402_SESSION_TOKEN=<token> \
  --env TOOLS402_CHAIN=base

# → 159 tools · see https://tools402.dev/docs/mcp