AI agents invoke next_day to trigger actions in Lemonade Stand MCP Server. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.
While the tool is part of a game simulation (low actual risk), it executes a game action whose effects depend on the current game state. It does not merely read data (Read), create reversible structures (Write), or permanently destroy data (Destructive). Advancing game state is an Execute-category operation—a triggered action with deterministic but contextual consequences.
From the tool's definition Tool name 'next_day' and description 'Advance to the next day' indicate the tool triggers state advancement in a game simulation.
Documented attack patterns abuse exactly the kind of access next_day 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 next_day:
{
"version": "1",
"default": "deny",
"tools": {
"next_day": {
"limits": [
{
"counter": "next_day_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}next_day stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.
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Advance to the next day. It is categorised as a Execute tool in the Lemonade Stand MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Lemonade Stand MCP Server MCP server in PolicyLayer and add a rule for next_day: 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.
next_day is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the next_day 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 next_day. 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.
next_day 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.
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5 Lemonade Stand MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.