everything-claude-code/skills/agent-payment-x402/SKILL.md

name, description, origin

name	description	origin
agent-payment-x402	Add x402 payment execution to AI agents — per-task budgets, spending controls, and non-custodial wallets via MCP tools. Use when agents need to pay for APIs, services, or other agents.	community

Agent Payment Execution (x402)

Enable AI agents to make autonomous 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 mcp-server-patterns skills.

Core Concepts

x402 Protocol

x402 extends HTTP 402 (Payment Required) into a machine-negotiable flow. When a server returns 402, the agent's payment tool automatically negotiates price, checks budget, signs a transaction, and retries — no human in the loop.

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; 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:

{
  "mcpServers": {
    "agentpay": {
      "command": "npx",
      "args": ["-y", "agentwallet-sdk"]
    }
  }
}

Available Tools

Tool	Purpose
get_balance	Check agent wallet balance
send_payment	Send payment to address or ENS
check_spending	Query remaining budget
set_policy	Configure spending limits
list_transactions	Audit trail of all payments

Example: Pay-Per-API-Call Agent

// In your CLAUDE.md or agent config:
// 1. Add agentpay MCP server (see above)
// 2. Set spending policy in your skill/hook:

// Hook: pre-tool check
if (toolName === "web_search" && apiCost > 0) {
  const budget = await mcp.call("agentpay", "check_spending");
  if (budget.remaining < apiCost) {
    return { error: "Budget exceeded for this task" };
  }
}

Best Practices

• Set budgets before delegation: When spawning sub-agents, attach a SpendingPolicy. Never give an agent unlimited spend.
• Audit trails: Use list_transactions in post-task hooks to log what was spent and why.
• Fail closed: If the payment tool is unreachable, block the paid action — don't fall back to unmetered access.
• Pair with security-review: Payment tools are high-privilege. Apply the same scrutiny as shell access.
• Test with testnets first: Use Base Sepolia for development; switch to Base mainnet for production.

Production Reference

• npm: agentwallet-sdk
• Merged into NVIDIA NeMo Agent Toolkit: PR #17 — x402 payment tool for NVIDIA's agent examples
• Protocol spec: x402.org