Send USDC on Base to any merchant payout address (the payoutAddress field shown by discover_merchants — NOT the merchantId). Use this whenever the user has confirmed they want to buy, purchase, pay, or send money for something. Gasless for you — Coal pays gas. Returns the on-chain tx hash. Auto-u...
Part of the Coal — Payments for AI agents server.
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AI agents use pay_merchant to initiate financial transactions through Coal — Payments for AI agents. Financial operations involve real money and are irreversible once processed. PolicyLayer blocks financial tools by default, requiring explicit human approval with transaction-level limits to prevent unauthorised spending.
pay_merchant moves real money. Without a policy, an autonomous agent could initiate transactions that drain accounts or exceed budgets. PolicyLayer blocks financial tools by default, requiring human-in-the-loop approval with configurable spending limits per transaction and per time window.
Financial tools involve real money. Block by default and require explicit human approval before enabling.
{
"version": "1",
"default": "deny",
"tools": {
"pay_merchant": {
"deny_if": [
{
"conditions": [],
"on_deny": "Requires human approval."
}
]
}
}
}See the full Coal — Payments for AI agents policy for all 13 tools.
These attack patterns abuse exactly the kind of access pay_merchant gives an agent. Each links to the full case and the policy that stops it:
Other financial tools across the catalogue. The same approach applies to each: deny by default, or require human approval.
Send USDC on Base to any merchant payout address (the payoutAddress field shown by discover_merchants — NOT the merchantId). Use this whenever the user has confirmed they want to buy, purchase, pay, or send money for something. Gasless for you — Coal pays gas. Returns the on-chain tx hash. Auto-uses the wallet key from the X-Coal-Agent-Key header in your Claude config (no need to ask the user for a key). Max $5 per tx. After this succeeds for a digital product, immediately call download_product with the returned tx hash to give the user their file.. It is categorised as a Financial tool in the Coal — Payments for AI agents MCP Server, which means it involves financial transactions. Block by default and require explicit approval.
Register the Coal — Payments for AI agents MCP server in PolicyLayer and add a rule for pay_merchant: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Coal — Payments for AI agents. Nothing to install.
pay_merchant is a Financial tool with critical risk. Critical-risk tools should be blocked by default and only enabled with explicit human approval.
Yes. Add a rate_limit block to the pay_merchant rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for pay_merchant. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
pay_merchant is provided by the Coal — Payments for AI agents MCP server (https://mcp.usecoal.xyz/api/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 13 Coal — Payments for AI agents tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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