AI agents call lean_hover_info 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.
Hover info in LSP is a diagnostic query that retrieves metadata about code elements (type information, documentation, etc.) without modifying or executing anything. No side effects or external operations are triggered. The empty description reduces confidence slightly, but the tool name and surrounding context strongly indicate a read-only diagnostic query.
From the tool's definition Tool name 'lean_hover_info' suggests retrieving hover information/tooltips from the Lean LSP server, a typical read operation.
Documented attack patterns abuse exactly the kind of access lean_hover_info 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_hover_info:
{
"version": "1",
"default": "deny",
"tools": {
"lean_hover_info": {}
}
}lean_hover_info is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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lean_hover_info. 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_hover_info: 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_hover_info 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_hover_info 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_hover_info. 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_hover_info 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.