AI agents invoke lean_run_code to trigger actions in Lean LSP MCP. 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.
The tool runs code ('run_code') which is inherently an Execute category action. While Lean is a theorem prover and not a shell or system command runner, executing arbitrary Lean code can trigger computations, side effects within the theorem prover, and produce unpredictable results depending on agent-supplied arguments.
From the tool's definition Tool name 'lean_run_code' indicates execution of code; combined with sibling context (Lean theorem prover interaction via LSP) and empty description, this appears to execute Lean code with effects determined by the code provided.
Documented attack patterns abuse exactly the kind of access lean_run_code gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Lean LSP MCP, and nothing reaches the server without passing your rules. This is the rule we recommend for lean_run_code:
{
"version": "1",
"default": "deny",
"tools": {
"lean_run_code": {
"limits": [
{
"counter": "lean_run_code_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}lean_run_code 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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lean_run_code. It is categorised as a Execute tool in the Lean LSP MCP MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Lean LSP MCP server in PolicyLayer and add a rule for lean_run_code: 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 Lean LSP MCP. Nothing to install.
lean_run_code 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 lean_run_code 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 lean_run_code. 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.
lean_run_code is provided by the Lean LSP MCP server (ooo0ooo/lean-lsp-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 23 Lean LSP MCP tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
23 Lean LSP MCP tools catalogued and risk-classified — across an index of 42,500+ MCP servers.