skill

n-payment

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Install instructions come from the README

Skills do not use an MCP config. Follow the steps in the README below; one-click install arrives with accounts.

README

synced Oct 14, 2026

n-payment

The chain-agnostic SDK for agentic payments — one fetchWithPayment(url) call, any chain, any protocol, any stablecoin.

npm install n-payment

import { createPaymentClient } from 'n-payment';

const client = createPaymentClient({
  chains: ['base-mainnet'],                 // any of 27+ supported chains
  ows:    { wallet: 'my-agent' },
});

// That's the whole API. SDK auto-detects 402 → signs → retries.
const res  = await client.fetchWithPayment('https://api.example.com/data');
const data = await res.json();

n-payment is a TypeScript SDK that turns HTTP 402 Payment Required into a one-line operation for AI agents. Your code calls a paywalled URL like any fetch. The SDK detects the payment protocol on the response, signs the right payment, and retries. It does not care whether the bill settles on an EVM chain, on XRPL, on Stellar, on a Cosmos chain, on Solana, or via a cross-chain bridge — the call site stays identical.

Why a chain-agnostic SDK matters for agents. Agents pick endpoints based on capability and price, not chain. A research agent calling 30 paid APIs in a session should not care which chain each merchant settles on. n-payment moves that decision out of agent code and into config — the same fetchWithPayment() call works for every supported rail.

What you get

One call, any rail. fetchWithPayment(url) works across x402, MPP, GOAT x402, XRPL, Stellar (x402 + MPP + Sessions), Cosmos MsgSend, Soroban payment channels, on-chain transferWithAuthorization, NTT bridge-as-payment, and more.
Protocol auto-detection. detectProtocol(response) reads the 402 headers and routes to the right adapter — no per-chain branching in your agent code.
Multichain wallet (OWS). A single CAIP-2-keyed wallet that signs across 11 chain families (EVM, Solana, XRPL, Cosmos, Bitcoin, Sui, Tron, TON, Spark, Filecoin, NEAR). One mnemonic, one config, every chain.
Policy & audit by default. Per-tx, per-hour, per-day spending caps; rate limits; trusted-facilitator allowlist; queryable on-disk audit log keyed by referenceKey.
Sub-cent micropayments. Off-chain vouchers (batch settlement) and Soroban payment channels for high-frequency / sub-cent flows.
Streaming + metered billing. StreamingPaymentManager settles usage at intervals against a budget envelope.
Yield-bearing treasury. Idle agent funds auto-supply to lending markets and auto-withdraw on demand. Your agent earns while it sleeps.
Sell APIs to other agents. createPaywall, paidTool, and a spec-compliant paid MCP server turn any HTTP service into an agent-discoverable, agent-payable endpoint in <20 lines.
AP2 verifiable intent. Cryptographic proof that a payment was authorized by a specific user mandate — survives audit and arbitration.
Cross-chain corridors. When the agent's holdings and the merchant's chain don't match, PayRouter picks the cheapest available bridge / swap automatically.

Everything is opt-in. The minimal config above pulls in zero peer dependencies beyond viem.

How `fetchWithPayment` works

Agent                                Paid API                          Adapter
  │                                    │                                  │
  │  1. GET /data ────────────────────▶│                                  │
  │                                    │                                  │
  │  2. ◀──── 402 + payment challenge ─│                                  │
  │     (header schema varies by protocol)                                │
  │                                                                       │
  │  3. detectProtocol(response)  ──▶  picks the right adapter            │
  │                                                                       │
  │  4. adapter.pay(challenge) ───────────────────────────────────────────▶
  │     (signs typed-data / tx / voucher / channel commitment)            │
  │                                                                       │
  │  5. GET /data + payment-proof header ▶ │                              │
  │                                       │  6. Verify (facilitator       │
  │                                       │     or on-chain)              │
  │  7. ◀──── 200 + body ────────────────│                                │

A few things worth calling out:

Step 3 is pure — the agent doesn't pick a chain. The adapter falls out of the response. Your agent doesn't need to know whether a given URL is paywalled by an EVM facilitator or a Stellar anchor.
Step 4 is bounded by policy. SpendingGuard.check() runs before signing. A blocked payment never touches a private key.
Step 5 retries on the same connection. No second round trip to discover the protocol again.

The full flow is one method on PaymentClient — you don't compose it manually.

Quickstarts

Pay for any paid API (consumer)

import { createPaymentClient } from 'n-payment';

const client = createPaymentClient({
  chains: ['base-mainnet'],
  ows:    { wallet: 'my-agent', privateKey: process.env.PRIVATE_KEY as `0x${string}` },
});

const res = await client.fetchWithPayment('https://api.example.com/data');
console.log(await res.json());

Want spending limits and an audit trail? Add policy:

const client = createPaymentClient({
  chains: ['base-mainnet'],
  ows:    { wallet: 'my-agent', privateKey: process.env.PRIVATE_KEY as `0x${string}` },
  policy: {
    maxPerTransaction:    100_000n,                // $0.10 per call (USDC, 6 decimals)
    maxPerHour:         1_000_000n,                // $1.00 / hour
    maxPerDay:         10_000_000n,                // $10.00 / day
    rateLimit:        { maxRequests: 100, windowMs: 60_000 },
    blocklist:        ['0xKnownScam...'],
    trustedFacilitators: ['https://api.cdp.coinbase.com/platform/v2/x402'],
  },
});

const res     = await client.fetchWithPayment('https://api.example.com/data');
const audit   = client.getGuard()?.getAudit();
const summary = audit?.getSpendingSummary(); // { total, count }

Sell APIs to other agents (provider)

import express from 'express';
import { createAgentProvider, paidTool, AgentCard } from 'n-payment';

const provider = createAgentProvider({
  name:        'WeatherBot',
  description: 'Weather data for AI agents',
  payTo:       '0xYourAddress',
  chain:       'base-mainnet',
  tools: [
    paidTool({
      name:        'forecast',
      description: 'Get weather forecast',
      price:        10_000n, // $0.01 USDC
      handler:      async ({ city }: { city: string }) => ({ city, temp: 22 }),
    }),
  ],
});

const app = express();
app.use(express.json());
app.use(provider.middleware());
app.get('/.well-known/agent.json', AgentCard.fromProvider(provider, 'https://your-api.com').handler());
app.listen(3000);

Ship a paid MCP server

Make any tool a paid MCP endpoint that any MCP-spec client (Claude Desktop, Cursor, ChatGPT, AWS Bedrock AgentCore, etc.) can discover and pay over.

import { createPaidMcpServer, paidTool } from 'n-payment/mcp';

const server = createPaidMcpServer({
  name:    'WeatherBot',
  payTo:   '0xYourAddress',
  chain:   'base-mainnet',
  tools: [
    paidTool({
      name:        'forecast',
      price:        10_000n,
      handler:      async ({ city }: { city: string }) => ({ city, temp: 22 }),
    }),
  ],
});

await server.listen(3000);

The host calls tools/list (sees price metadata), calls tools/call (gets MCP error -32402 with the payment envelope), the host's wallet signs, the call retries with the proof header, and the response streams back. Spec-compliant. One file. No facilitator to self-host.

claude mcp add --transport http weather http://localhost:3000

server.toExpressMiddleware() and server.handle(req: Request) (Fetch-API) are also exposed for Cloudflare Workers / Bun / Deno.

Agentic primitives

These are protocol-agnostic — they compose with any adapter the SDK ships.

Multichain wallet — one mnemonic, eleven chain families

import { OWSWallet, ows } from 'n-payment';

const w = new OWSWallet({ wallet: 'agent-treasury' });

// Same method, four chain families.
await w.getAddress('eip155:8453');         // 0x...
await w.getAddress('xrpl:mainnet');        // r...
await w.getAddress('solana:mainnet');      // 7xKX...
await w.getAddress('cosmos:interwoven-1'); // init1...

// Multi-agent isolation: scoped, revocable, policy-bound API keys.
const policy = await ows.createPolicy({ allowChains: ['eip155:8453'], maxValuePerTx: '5.00 USD' });
const key    = await ows.createApiKey({ name: 'sub-agent-A', wallets: ['agent-treasury'], policy });
// → hand `key.token` to a sub-agent. Revoke any time without touching the master mnemonic.

The wallet is CAIP-2-native: every method takes a chain ID as a string and dispatches to the right family — eip155, solana, xrpl, cosmos, bip122, sui, tron, ton, spark, filecoin, near. Chains with payrouter rails today get end-to-end fetchWithPayment support; other families ship wallet-bound (address derivation + signing) so your agent can already prove identity on every chain it touches.

Policy engine + audit log

import { PolicyEngine, AuditLog, SpendingGuard } from 'n-payment';

const engine = PolicyEngine.fromConfig({
  maxPerTransaction: 100_000n,
  maxPerDay:         10_000_000n,
  rateLimit:         { maxRequests: 100, windowMs: 60_000 },
});

const guard = new SpendingGuard(engine, new AuditLog());
const decision = guard.check({ amount: 50_000n, recipient: '0x...' });
// decision.allowed === true | false; decision.reason explains why.

Wired automatically inside PaymentClient when you pass policy: {…}. The audit log is queryable by referenceKey so you can reconcile agent spend against merchant orders.

Batch settlement (sub-cent payments)

import { BatchSettlementManager } from 'n-payment';

const batch = new BatchSettlementManager();

const session = batch.openSession({
  chain:         'base-mainnet',
  budget:         1_000_000n, // $1.00
  escrowContract: '0x...',
});

// Each API call: sign an off-chain voucher (zero gas).
const voucher = batch.signVoucher(session.id, 100n); // $0.0001

// Seller batch-settles many vouchers in one tx later.

Streaming payments

import { StreamingPaymentManager } from 'n-payment';

const streaming = new StreamingPaymentManager();

const stream = streaming.createStream({
  provider:        '0xProvider',
  chain:           'base-mainnet',
  budget:          5_000_000n,   // $5.00
  intervalMs:      60_000,        // settle every minute
  maxPerInterval:  100_000n,      // ≤ $0.10 / minute
});

streaming.recordUsage(stream.id, 1_000n); // $0.001
streaming.settleInterval(stream.id);

Verifiable agent authorization (AP2)

import { AP2Client } from 'n-payment';

const ap2 = new AP2Client({ agentId: 'my-agent-123' });

// User authorizes the agent with a budget and expiry.
const mandate = ap2.createCheckoutMandate({
  maxBudget: 5_000_000n,            // $5.00
  expiresAt: Date.now() + 3_600_000,
});

// Agent shops, then closes the mandate against a specific cart.
const closed = ap2.closeCheckoutMandate(mandate.id, {
  items:    [{ name: 'Weather API', price: 10_000n, quantity: 1 }],
  total:    10_000n,
  merchant: '0xProvider',
});

// Issue a payment mandate carrying cryptographic proof of authorization.
const payment = ap2.createPaymentMandate(closed.id, 10_000n, 'x402');

Multi-agent delegation

import { createAgentClient } from 'n-payment';

const leader      = createAgentClient({ chain: 'base-mainnet', wallet: 'leader-agent' });
const budget      = leader.createDelegation(5_000_000); // $5.00
const workerSlice = leader.delegate(budget, 1_000_000); // $1.00 to worker

const result = await leader.call('https://api.example.com/data', {
  delegationCtx: workerSlice,
});

Yield-bearing treasury

Idle agent funds can auto-supply to a lending market (so they earn while sleeping) and auto-withdraw on demand:

const client = createPaymentClient({
  chains: ['base-mainnet'],
  ows:    { wallet: 'my-agent', privateKey: process.env.PRIVATE_KEY as `0x${string}` },
  aave: {
    autoYield:        true,            // supply idle USDC
    minIdleBalance:   10_000_000n,     // keep $10 liquid
    borrowEnabled:    true,            // borrow stablecoin against collateral instead of selling
    maxLTV:           70,
    preferGho:        true,            // pay with GHO when accepted (gasless via EIP-2612)
  },
});

await client.fetchWithPayment('https://paid-api.com/data');
const state = client.aave?.yield.getState();
// state.supplied, state.yieldEarned

Flash-mint batched payments and ERC-4626 vault management ship in the same module.

Cross-chain corridor selection

When the agent holds funds on one chain and the merchant wants payment on another, the SDK can route automatically:

import { selectRlusdCorridor } from 'n-payment';

const decision = selectRlusdCorridor({
  buyerHoldings: { 'optimism-mainnet': 5_000_000n },
  merchantWants: { chain: 'base-mainnet', amount: 1_500_000n },
});
// → { path: 'ntt-bridge', latencyMs: 75_000, ... }

Equivalent corridor selectors exist for Stellar multi-stable swaps (selectAsset), Cosmos USDC→iUSD bridging (selectIusdCorridor), and Mento corridors. PayRouter picks based on holdings, fees, and slippage caps you set in config.

Selling: middleware for any HTTP framework

import express from 'express';
import { createPaywall, createHealthEndpoint } from 'n-payment';

const config = {
  routes: {
    'GET /api/data': {
      price:       '10000', // $0.01 USDC, 6 decimals
      description: 'Premium data endpoint',
      x402:        { payTo: '0xYourAddress' },
    },
  },
};

const app = express();
app.use(express.json());
app.use(createPaywall(config));
app.get('/health',   createHealthEndpoint(config));
app.get('/api/data', (_req, res) => res.json({ result: 'paid content' }));
app.listen(3000);

Add an MPP block to the same route to accept both protocols at once:

'GET /api/data': {
  price: '10000',
  x402:  { payTo: '0xYourAddress' },
  mpp:   { currency: '0x20c0...', recipient: '0xYourAddress' },
}

Receive RLUSD on XRPL with auto-trustline

Add an xrpl block to a route to accept RLUSD via the T54 facilitator on testnet (xrpl:1) or mainnet (xrpl:0). Setting config.xrpl.seed (or .owsWallet) lets the SDK auto-create the receiver's RLUSD trustline on the first 402 — useful on testnet and for demos. Omit it for production fail-fast mode (paywall returns 503 XRPL_MERCHANT_NO_TRUSTLINE until the trustline is pre-created).

app.use(createPaywall({
  routes: {
    'GET /paid': {
      price: '0.01', // 0.01 RLUSD
      xrpl:  { payTo: 'rYourReceiverAddress', network: 'xrpl:1', asset: 'RLUSD' },
    },
  },
  // optional: enables one-time TrustSet on first call
  xrpl: { seed: process.env.XRPL_RECEIVER_SEED },
}));

Need finer-grained access control? Compose the paywall with a KYA / KYC gate:

import { StellarKyaGate } from 'n-payment';

const gate = new StellarKyaGate({ minKyaTier: 2 });
app.get('/skill', gate.middleware(), (_req, res) => res.json({ data: 'gated' }));

Cash out to fiat via MoneyGram on Stellar (SEP-10 / SEP-24 / SEP-31 / SEP-38)

An agent earning USDC or MGUSD on Stellar can cash out to physical fiat at any of MoneyGram's ~174 supported countries in one line. The same facade covers pre-flight FX quotes (SEP-38) and agent-to-agent direct payment (SEP-31). Testnet dev flow points at SDF's reference test anchor at testanchor.stellar.org — no MoneyGram allowlist required.

import { stellarAgentKit } from 'n-payment';

const kit    = stellarAgentKit(signer);                        // mainnet default
const quote  = await kit.quote({ amount: '10.00', asset: 'USDC', fiat: 'USD', country: 'US' });
const cash   = await kit.cashOut('10.00', 'USDC', 'USD');      // opens moreInfoUrl for KYC + retail pickup

See ~/.kiro/skills/moneygram-stellar-agent-kit/SKILL.md for the full mainnet + testnet quickstart.

Capability matrix

Chains and protocols are config knobs. The agent code does not change.

Family	Chains	Protocols spoken	Notable capabilities
EVM	Base, Arbitrum, BNB, Optimism, Ink, Unichain, Ethereum, GOAT, Morph, SpaceRouter chains, Flare, Songbird, Coston2, fee-abstracted L2s	`x402`, MPP, EIP-3009 sponsored, EIP-2612 permit, Permit2, fee-currency adapters	gas sponsoring, gasless payments, yield treasury
Cosmos-SDK	Initia (and any `cosmos:*` namespace OWS supports)	`cosmos-msgsend`	USDC→native-stable bridge corridor
XRPL	XRPL mainnet/testnet	XRPL native, x402 (T54 / RLUSD-first), RLUSD payments, payment channels	invoice-bound presigned blobs settled via T54 facilitator; XRP↔RLUSD AMM auto-swap; vault treasury
Stellar	Stellar mainnet/testnet	x402, MPP, MPP Session (Soroban payment channels)	sub-cent off-chain commitments, multi-stable swap
Solana	Solana mainnet/devnet	x402	SPL transfers
Cross-chain	Any pair the corridor solver can connect	Wormhole NTT, LayerZero V2 OFT, Skip API, Mento	bridge-as-payment, atomic mint-and-pay

A new chain or protocol is added by implementing one PaymentAdapter interface (detect() + pay()). Nothing in PaymentClient or in your agent code changes.

Concrete chain identifiers (full list in CHAINS):

base-mainnet, base-sepolia, arbitrum-sepolia, bnb-mainnet, bnb-testnet,
ethereum-mainnet, optimism-mainnet, ink-mainnet, unichain-mainnet,
goat-mainnet, goat-testnet, morph-mainnet, morph-hoodi-testnet,
creditcoin-mainnet, creditcoin-testnet,
flare-mainnet, flare-songbird-mainnet, flare-coston2-testnet,
xrpl-mainnet, xrpl-testnet,
stellar-mainnet, stellar-testnet,
solana-mainnet, solana-devnet,
tempo-mainnet, tempo-testnet,
initia-mainnet, initia-testnet,
celo-mainnet, celo-sepolia

Pick whichever subset your agent needs in the chains: field.

Architecture

┌─────────────────────────────────────────────────────────────────────┐
│                        Your agent code                              │
│                fetchWithPayment(url)                                │
├─────────────────────────────────────────────────────────────────────┤
│  Policy Engine  →  Spending Guard  →  Audit Log                     │
├─────────────────────────────────────────────────────────────────────┤
│  Yield Treasury │ Batch Settlement │ Streaming │ AP2 Verifiable     │
├─────────────────────────────────────────────────────────────────────┤
│  detectProtocol(response)  →  PaymentAdapter dispatch               │
├─────────────────────────────────────────────────────────────────────┤
│  x402 │ MPP │ XRPL │ Stellar (x402+MPP+Sessions) │ EIP-3009 │ NTT  │
│  Solana x402 │ Cosmos MsgSend │ payment channels │ on-chain settle │
├─────────────────────────────────────────────────────────────────────┤
│  OWSWallet (CAIP-2 multichain)  │  Permit2 / EIP-3009 / EIP-712     │
└─────────────────────────────────────────────────────────────────────┘

All boxes are independently testable units. The agent only ever talks to the top one.

Configuration reference

createPaymentClient({
  // Required
  chains: ['base-mainnet'],
  ows:    { wallet: 'name', privateKey: '0x...' },

  // Optional
  protocol:        'auto',                                // 'x402' | 'mpp' | 'auto'
  policy:          { maxPerTransaction, maxPerDay, rateLimit, blocklist },
  ap2:             { agentId, signingKey },               // verifiable intent
  batchSettlement: { enabled: true },                     // sub-cent vouchers
  streaming:       { defaultInterval: 60_000 },           // metered billing
  x402:            { usePermit2: true },                  // Permit2 for any ERC-20

  // Treasury / corridors (all optional — opt in only what you need)
  aave:        { autoYield, minIdleBalance, borrowEnabled, preferGho, delegation },
  xrpl:        { seed, autoSwap, treasury, facilitatorUrl, sourceTag },
  stellar:     { secretKey, channelsApiKey },
  solana:      { keypair },
  morph:       { accessKey, secretKey, facilitatorUrl },
  goat:        { apiKey, apiSecret, merchantId, autoFund },
  flare:       { network, x402, gasless },
  initia:      { network, mnemonic },
  spacerouter: { region, ipType, autoEscrow },
  wormhole:    { signers, maxPerTransfer, maxPerDay },
  circle:      { apiKey, environment },
});

Each block is independent — leaving one out simply disables that adapter.

API reference

Core

Export	Purpose
`createPaymentClient(c)`	Make a payment client (auto-detects protocol)
`createPaywall(c)`	Express paywall middleware
`createHealthEndpoint(c)`	Health / pricing endpoint
`detectProtocol(res)`	Detect 402 protocol from a `Response`
`CHAINS`, `getChain(k)`	Chain registry + lookup

Wallet

Export	Purpose
`OWSWallet({ wallet, privateKey? })`	CAIP-2-keyed multichain wallet
`ows` (lifecycle namespace)	Create / import / export / restore / rotate / lock / discover; policy & API-key CRUD
`parseCaip2`, `resolveFamily`	CAIP-2 parsing helpers

Agent commerce

Export	Purpose
`createAgentProvider(c)`	Sell services with paywall gating
`createAgentClient(c)`	Buy services with discovery
`paidTool(def)`	Define a paid tool (MCP-compatible)
`createPaidMcpServer(c)`	Spec-compliant paid MCP server
`AgentCard.fromProvider()`	Generate A2A Agent Card
`PricingEngine`	Dynamic pricing (demand / reputation / outcome)
`SessionManager`	Micropayment sessions
`EscrowManager`	ERC-8183 programmable escrow
`PaymentNegotiator`	Auto-select direct / escrow / credit
`ReputationRouter`	Trust-weighted provider selection
`DelegationManager`	Multi-agent budget chains

Settlement & policy

Export	Purpose
`BatchSettlementManager`	Off-chain vouchers + cumulative settlement
`StreamingPaymentManager`	Interval-based streaming payments
`Permit2Signer`	EIP-712 Permit2 for any ERC-20
`PolicyEngine`	Spending limits, rate limits, blocklist
`AuditLog`	Queryable payment history (by `referenceKey`)
`SpendingGuard`	Wraps payments with policy enforcement

AP2 protocol

Export	Purpose
`AP2Client`	Agent Payments Protocol (Google / FIDO)
`VerifiableIntentSigner`	Tamper-proof agent action authorization

Adapters (auto-loaded by `PaymentClient`)

X402Adapter, MppAdapter, GoatAdapter, XrplAdapter, StellarX402Adapter, StellarMppAdapter, MorphX402Adapter, SpaceRouterAdapter, FlareX402Adapter, WormholeNttAdapter, RlusdExactAdapter, InitiaIusdAdapter, CeloFeeAbstractedAdapter, CircleGatewayAdapter, SolanaX402Adapter, AaveGhoAdapter.

You almost never reference these directly — PaymentClient picks the right one based on the chains you configure and the 402 challenge it sees.

Error handling

import {
  NPaymentError,
  InsufficientBalanceError,
  AdapterNotFoundError,
  ChallengeParseError,
} from 'n-payment';

try {
  await client.fetchWithPayment(url);
} catch (err) {
  if (err instanceof InsufficientBalanceError) {
    console.log('Fund wallet:', err.hint);
  } else if (err instanceof AdapterNotFoundError) {
    console.log('Wrong chain config:', err.hint);
  } else if (err instanceof ChallengeParseError) {
    console.log('Malformed 402 from server:', err.hint);
  } else if (err instanceof NPaymentError) {
    console.log(`${err.code}: ${err.message}`);
  } else {
    throw err;
  }
}

Every error carries a code and an actionable hint. The audit log records the failure reason regardless of whether the payment was attempted.

Agent decision guide

You want to…	Use this
Pay for any paid API automatically	`createPaymentClient()` → `fetchWithPayment(url)`
Sell your API for crypto	`createAgentProvider()` + `paidTool()`
Ship a paid MCP server	`createPaidMcpServer()` from `n-payment/mcp`
Find services to buy	`createAgentClient()` → `discover(query)`
Limit spending	`policy: { maxPerDay, rateLimit, blocklist }`
Sub-cent micropayments	`BatchSettlementManager`
Streaming / metered billing	`StreamingPaymentManager`
Multi-agent budget sharing	`DelegationManager` or `ows.createApiKey({ policy })`
Escrow for high-value tasks	`EscrowManager` or `TrustlessEscrowManager`
Prove user authorization (AP2)	`AP2Client` + `VerifiableIntentSigner`
Earn yield on idle funds	`aave: { autoYield: true }`
Pay across chains automatically	`PayRouter` corridor selectors + adapter-specific bridge config

For agent frameworks

n-payment ships as a single import, which makes it trivial to wrap as a tool in any framework.

LangChain / CrewAI / AutoGen

import { createPaymentClient } from 'n-payment';
import { Tool } from 'langchain/tools';

class PaidApiTool extends Tool {
  name        = 'pay_for_api';
  description = 'Call any paid API; SDK auto-handles HTTP 402 across any supported chain.';
  private client = createPaymentClient({ chains: ['base-mainnet'], ows: { wallet: 'agent' } });

  async _call(url: string) {
    const res = await this.client.fetchWithPayment(url);
    return JSON.stringify(await res.json());
  }
}

Model Context Protocol

createPaidMcpServer() (above) is what you ship to MCP-aware hosts. Any tool defined with paidTool() becomes spec-compliant tools/list + tools/call with x402 monetization.

Kiro CLI / Claude Code

cp SKILL.md ~/.kiro/skills/agent-payment/SKILL.md

The skill exposes 19 payment tools (pay, balance, paywall, discover, negotiate, session, escrow, delegate, identity, reputation, feedback, off-ramp, multi-agent coordination, …).

Why agents need a chain-agnostic SDK

Chain selection happens at config, not at call time. Agents that hard-code chains break the moment a service prices a call differently on another rail.
A single audit trail across rails. Reconcile spend by referenceKey regardless of which chain the proof landed on.
One wallet, many identities. OWS-bound CAIP-2 addresses on 11 chain families let an agent prove identity wherever it needs to without juggling key material.
Policy is the same everywhere. maxPerDay enforced on EVM is the same maxPerDay enforced on XRPL — the guard runs above the adapter.
Cross-chain corridors are an SDK concern, not an agent concern. When the agent's wallet and the merchant's chain disagree, a corridor selector picks a bridge / swap behind the scenes.

If your agent is going to call dozens of paid APIs across a session, you do not want chain logic in your prompt context. You want a function that takes a URL and returns a body.

That is fetchWithPayment(url).

License

MIT

n-payment

Set up

README

n-payment

What you get

How fetchWithPayment works

Quickstarts

Pay for any paid API (consumer)

Sell APIs to other agents (provider)

Ship a paid MCP server

Agentic primitives

Multichain wallet — one mnemonic, eleven chain families

Policy engine + audit log

Batch settlement (sub-cent payments)

Streaming payments

Verifiable agent authorization (AP2)

Multi-agent delegation

Yield-bearing treasury

Cross-chain corridor selection

Selling: middleware for any HTTP framework

Receive RLUSD on XRPL with auto-trustline

Cash out to fiat via MoneyGram on Stellar (SEP-10 / SEP-24 / SEP-31 / SEP-38)

Capability matrix

Architecture

Configuration reference

API reference

Core

Wallet

Agent commerce

Settlement & policy

AP2 protocol

Adapters (auto-loaded by PaymentClient)

Error handling

Agent decision guide

For agent frameworks

LangChain / CrewAI / AutoGen

Model Context Protocol

Kiro CLI / Claude Code

Why agents need a chain-agnostic SDK

License

How `fetchWithPayment` works

Adapters (auto-loaded by `PaymentClient`)