agent-payment-x402

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• SKILL.md

SKILL.md (first lines)

# Agent Payment Execution (x402)

Enable AI agents to make policy-gated payments with built-in spending controls. Uses the x402 HTTP payment protocol and MCP tools so agents can pay for external services, APIs, or other agents without custodial risk.

## When to Use

Use when: your agent needs to pay for an API call, purchase a service, settle with another agent, enforce per-task spending limits, or manage a non-custodial wallet. Pairs naturally with cost-aware-llm-pipeline and security-review skills.

## Decision Tree

Choose the integration path based on whether your agent is buying access to a paid API or charging others for one:

| Need | Recommended path |
|------|------------------|
| Agent pays a 402-gated API on Base or another agentwallet-supported chain | Use `agentwallet-sdk` as an MCP payment server with strict spending policy |
| Agent pays a 402-gated API on X Layer | Use OKX Agent Payments Protocol from `okx/onchainos-skills`; `okx-x402-payment` is a deprecated legacy alias |
| Agent pays a 402-gated API on Solana or another x402 v2 network | Wrap the agent's HTTP client with the upstream `@x402/fetch` or `@x402/axios` package and register the EVM/SVM schemes; the resource server's facilitator verifies and settles |
| API charges agents on Solana or multiple networks (TypeScript, Python, or Go) | Use the upstream x402 middleware from `x402-foundation/x402` — `@x402/express`, `@x402/hono`, `@x402/next`, or `@x402/fastify` for TypeScript, `x402` for Python, `github.com/x402-foundation/x402/go/v2` for Go |
| TypeScript API charges agents | Use OKX Payments TypeScript seller SDK docs for Express, Hono, Fastify, or Next.js |
| Go API charges agents | Use OKX Payments Go seller SDK docs for Gin, Echo, or `net/http` |
| Rust API charges agents | Use OKX Payments Rust seller SDK docs for Axum |
| Java API charges agents | Use OKX Payments Java seller SDK docs for Spring Boot 2/3, Java EE, or Jakarta |
| Python API charges agents | Check the current OKX Payments repository before implementation; a Python seller guide may not be available |

## Supported Networks

- `agentwallet-sdk`: use the package docs to confirm current network coverage before production. Base Sepolia is the safest development default; Base mainnet is the production path called out by the original skill.
- OKX Payments / X Layer: current seller docs target X Layer (`eip155:196`) and USDT0 settlement. Fetch current SDK docs before generating production code because payment packages and facilitator behavior can change quickly.
- Upstream x402 packages: multi-network by design — one route can advertise Base and Solana simultaneously and let the buyer pick. The packages default to the `x402.org` facilitator, which is testnet-only (Base Sepolia `eip155:84532`, Solana devnet `solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1`, plus Stellar, Aptos, Hedera, and XRPL testnets) and is not intended for mainnet routes. For mainnet (`solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp` for Solana), either self-facilitate, run your own facilitator, or pick a hosted one from the upstream facilitator list — see the facilitator comparison under Option C. Confirm live coverage at the facilitator's `/supported` endpoint before production rather than hardcoding it here.

## How It Works

### x402 Protocol
x402 extends HTTP 402 (Payment Required) into a machine-negotiable flow. When a server returns `402`, the agent's payment tool negotiates price, checks budget, signs a transaction, and retries only inside the policy and confirmation boundary set by the orchestrator.

### Spending Controls
Every payment tool call enforces a `SpendingPolicy`:
- **Per-task budget** — max spend for a single agent action
- **Per-session budget** — cumulative limit across an entire session
- **Allowlisted recipients** — restrict which addresses/services the agent can pay
- **Rate limits** — max transactions per minute/hour

### Non-Custodial Wallets
Agents hold their own keys via ERC-4337 smart accounts. The orchestrator sets policy before delegation; the agent can only spend within bounds. No pooled funds, no custodial risk.

## MCP Integration

The payment layer exposes standard MCP tools that slot into any Claude Code or agent harness setup.

> **Security note**: Always pin the package version. This tool manages private keys — unpinned `npx` installs introduce supply-chain risk.

### Option A: agentwallet-sdk (Base / multi-chain)

```json
{
  "mcpServers": {
    "agentpay": {
      "command": "npx",
      "args": ["agentwallet-sdk@6.0.0"]
    }
  }
}
```

### Available Tools (agent-callable)

| Tool | Purpose |
|------|---------|
| `get_balance` | Check agent wallet balance |
| `send_payment` | Send payment to address or ENS |
| `check_spending` | Query remaining budget |
| `list_transactions` | Audit trail of all payments |

> **Note**: Spending policy is set by the **orchestrator** before delegating to the agent — not by the agent itself. This prevents agents from escalating their own spending limits. Configure policy via `set_policy` in your orchestration layer or pre-task hook, never as an agent-callable tool.

### Option B: OKX Agent Payments Protocol (X Layer)

Use this path for X Layer x402, Multi-Party Payment (MPP), session payment, charge, and A2A charge flows.

For buyer-side agent flows:

1. Install or reference the current `okx/onchainos-skills` repository.
2. Use `skills/okx-agent-payments-protocol/SKILL.md` as the dispatcher.
3. Treat `skills/okx-x402-payment/SKILL.md` as a deprecated compatibility alias, not as the canonical skill.
4. Require explicit user confirmation before wallet status checks or payment actions. Do not hide payment execution behind a generic tool call.

For seller-side API flows, fetch the latest language-specific guide before generating code:

| Runtime | Current guide |
|---------|---------------|
| TypeScript | `https://raw.githubusercontent.com/okx/payments/main/typescript/SELLER.md` |
| Go | `https://raw.githubusercontent.com/okx/payments/main/go/x402/SELLER.md` |
| Rust | `https://raw.githubusercontent.com/okx/payments/main/rust/x402/SELLER.md` |
| Java | `https://raw.githubusercontent.com/okx/payments/main/java/SELLER.md` |

Do not copy examples from older docs without checking the current OKX repository. Current OKX guidance uses `okx-agent-payments-protocol` as the dispatcher, and Java seller docs are now available.

### Option C: Upstream x402 packages (Solana + Base/EVM)

Use this path when the agent pays — or your API charges — on Solana, Base, or another network the upstream protocol implementation supports. The canonical x402 monorepo at [`x402-foundation/x402`](https://github.com/x402-foundation/x402) is actively maintained and publishes the client and middleware packages directly. Unlike Options A and B this is not a separate MCP server — you wrap the agent's own HTTP client, and a facilitator chosen by the resource server verifies and settles.

For buyer-side agent flows:

1. Start from the maintained examples in [`examples/typescript/clients`](https://github.com/x402-foundation/x402/tree/main/examples/typescript/clients) (fetch, axios, MCP) rather than copying snippets from older docs.
2. Require explicit user confirmation before signing or submitting the first paid request, exactly as Option B requires for OKX flows. Do not hide payment execution behind a generic tool call.
3. Pin package versions (for example `@x402/fetch@2.22.0`); all upstream packages version in lockstep.
4. Enforce your budget with a `PaymentPolicy` registered on the client, so the check runs against the server's actual challenge on every call. A budget compared against a number you passed in yourself proves nothing — the amount, asset, and network all come from the server, so all three must be validated before a signature exists.

5. Configure an exact resource-origin allowlist separately from recipient and budget policy. All payment-enabled fetches below refuse redirects. Session approval names the approved origins, networks, assets, recipients, and human-unit spending caps; concurrent calls share one decision. Keep this client and its policy private to the orchestrator.

```typescript
import { x402Client, wrapFetchWithPayment } from "@x402/fetch";
import { ExactEvmScheme } from "@x402/evm/exact/client";
import { ExactSvmScheme } from "@x402/svm/exact/client";
import { privateKeyToAccount } from "viem/accounts";
import { createKeyPairSignerFromBytes } from "@solana/kit";
import { base58 } from "@scure/base";

// Signer keys belong to the ORCHESTRATOR's env — never hardcoded, never agent-writable.

From mdnaimul22/human-skills, MIT.

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