expression_evaluator · Math MCP Server MCP: Risk & Policy

WHAT IT DOES

What expression_evaluator does on Math MCP Server

AI agents invoke expression_evaluator to trigger actions in Math 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.

WHY IT NEEDS A POLICY

Why expression_evaluator needs a policy

An 'expression_evaluator' tool likely executes or interprets mathematical expressions, potentially including arbitrary code depending on implementation. Given the empty description, there is uncertainty, but expression evaluation commonly involves executing parsed input which could be misused (e.g., code injection). The most severe plausible category given the name and context is Execute.

From the tool's definition Tool name 'expression_evaluator' on a math server with sibling tools like 'calculus_engine' and 'mathematical_functions'; description is empty and uninformative.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

expression_evaluator Rate-limited

expression_evaluator 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.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "expression_evaluator": {
      "limits": [
        {
          "counter": "expression_evaluator_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Math MCP Server, so you can run agents against it safely.

FAQ

Questions about expression_evaluator

What does the expression_evaluator tool do? +

expression_evaluator. It is categorised as a Execute tool in the Math MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on expression_evaluator? +

Register the Math MCP Server MCP server in PolicyLayer and add a rule for expression_evaluator: 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 Math MCP Server. Nothing to install.

What risk level is expression_evaluator? +

expression_evaluator is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit expression_evaluator? +

Yes. Add a rate_limit block to the expression_evaluator 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.

How do I block expression_evaluator completely? +

Set action: deny in the PolicyLayer policy for expression_evaluator. 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.

What MCP server provides expression_evaluator? +

expression_evaluator is provided by the Math MCP Server MCP server (111-test-111/math-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.