Purchase supplies for the lemonade stand
AI agents use buy_supplies to commit financial operations through Lemonade Stand MCP Server — usually the final step of a payment, billing, or trading workflow. A call moves real money.
The tool purchases supplies, which constitutes a financial transaction within the game simulation. While the money is fictional/simulated, the action models a financial commitment (spending in-game currency on inventory). Given the server is a business simulation game, the financial impact is contained to the game state.
From the tool's definition 'Purchase supplies' — explicitly buys goods, committing simulated financial resources
Documented attack patterns abuse exactly the kind of access buy_supplies gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Lemonade Stand MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for buy_supplies:
{
"version": "1",
"default": "deny",
"tools": {
"buy_supplies": {
"deny_if": [
{
"conditions": [],
"on_deny": "Requires human approval."
}
]
}
}
}Any call to buy_supplies is blocked until a human approves it. The rest of the server keeps working.
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Purchase supplies for the lemonade stand. It is categorised as a Financial tool in the Lemonade Stand MCP Server MCP Server, which means it involves financial transactions. Block by default and require explicit approval.
Register the Lemonade Stand MCP Server MCP server in PolicyLayer and add a rule for buy_supplies: 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 Lemonade Stand MCP Server. Nothing to install.
buy_supplies 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 buy_supplies 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 buy_supplies. 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.
buy_supplies is provided by the Lemonade Stand MCP Server MCP server (jimmcq/lemonade-stand-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Lemonade Stand MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
5 Lemonade Stand MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.