Detect payment protocol for any MCP server and route to the correct payment execution. Supports x402 (USDC on Base), MPP (Stripe), and prepaid API keys.
Risk signalsAccepts URL/endpoint input (endpoint) · Accepts raw HTML/template content (payload)
Part of the Library server.
Free to start. No card required.
AI agents use checkout to create or modify resources in Library. 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 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 Library.
Write tools can modify data. A rate limit prevents runaway bulk operations from AI agents.
{
"version": "1",
"default": "deny",
"tools": {
"checkout": {
"limits": [
{
"counter": "checkout_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}See the full Library policy for all 4 tools.
These attack patterns abuse exactly the kind of access 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.
Detect payment protocol for any MCP server and route to the correct payment execution. Supports x402 (USDC on Base), MPP (Stripe), and prepaid API keys.. It is categorised as a Write tool in the Library MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Library MCP server in PolicyLayer and add a rule for 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 Library. Nothing to install.
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 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 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.
checkout is provided by the Library MCP server (https://librarymcp.vercel.app/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 4 Library tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
4,600+ MCP servers and 31,000+ tools scanned and risk-classified.