Create a Coal checkout session to pay for a product or amount. Settles in USDC on Base (~2s). Returns a checkout URL. Needs a Coal API key — set once via Claude config header X-Coal-Api-Key:YOUR_KEY, or pass per-call as coalApiKey. Get one at https://usecoal.xyz/console/keys.
Part of the Coal — Payments for AI agents server.
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AI agents use create_checkout to create or modify resources in Coal — Payments for AI agents. Write operations carry medium risk because an autonomous agent could trigger bulk unintended modifications. Rate limits prevent a single agent session from making hundreds of changes in rapid succession. Argument validation ensures the agent passes expected values.
Without a policy, an AI agent could call create_checkout repeatedly, creating or modifying resources faster than any human could review. PolicyLayer's rate limiting ensures write operations happen at a controlled pace, and argument validation catches malformed or unexpected inputs before they reach Coal — Payments for AI agents.
Write tools can modify data. A rate limit prevents runaway bulk operations from AI agents.
{
"version": "1",
"default": "deny",
"tools": {
"create_checkout": {
"limits": [
{
"counter": "create_checkout_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}See the full Coal — Payments for AI agents policy for all 13 tools.
These attack patterns abuse exactly the kind of access create_checkout gives an agent. Each links to the full case and the policy that stops it:
Other write tools across the catalogue. The same approach applies to each: rate-limit and validate the arguments.
Create a Coal checkout session to pay for a product or amount. Settles in USDC on Base (~2s). Returns a checkout URL. Needs a Coal API key — set once via Claude config header X-Coal-Api-Key:YOUR_KEY, or pass per-call as coalApiKey. Get one at https://usecoal.xyz/console/keys.. It is categorised as a Write tool in the Coal — Payments for AI agents MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Coal — Payments for AI agents MCP server in PolicyLayer and add a rule for create_checkout: 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.
create_checkout is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the create_checkout 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 create_checkout. 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.
create_checkout 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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