AI agents call lean_file_outline to retrieve information from Lean Lsp without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
An outline operation retrieves and presents the hierarchical structure of a Lean file (declarations, definitions, theorems) without executing code, modifying files, or triggering external side effects. This is a read-only informational query typical of language server protocol (LSP) operations. No destructive, financial, or execute-class operations are implied.
From the tool's definition Tool name 'lean_file_outline' and server context (agentic interaction with Lean theorem prover) suggest retrieval of structural information. Description is empty, but 'outline' conventionally means extracting/displaying structure without modification.
Documented attack patterns abuse exactly the kind of access lean_file_outline gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Lean Lsp, and nothing reaches the server without passing your rules. This is the rule we recommend for lean_file_outline:
{
"version": "1",
"default": "deny",
"tools": {
"lean_file_outline": {}
}
}lean_file_outline is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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lean_file_outline. It is categorised as a Read tool in the Lean Lsp MCP Server, which means it retrieves data without modifying state.
Register the Lean Lsp MCP server in PolicyLayer and add a rule for lean_file_outline: 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. Nothing to install.
lean_file_outline is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the lean_file_outline 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_file_outline. 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_file_outline is provided by the Lean Lsp MCP server (project-numina/lean-lsp-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Lean Lsp, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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22 Lean Lsp tools catalogued and risk-classified — across an index of 43,000+ MCP servers.