calculator · Simple MCP Server MCP: Risk & Policy

WHAT IT DOES

What calculator does on Simple MCP Server

AI agents invoke calculator to trigger actions in Simple 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 calculator needs a policy

A calculator tool evaluates mathematical expressions or operations provided as arguments. While it doesn't modify data or delete anything, it executes logic (potentially arbitrary expression evaluation) whose output depends on inputs. If implemented as an expression evaluator (e.g., eval-based), it could be exploited for code execution.

From the tool's definition "Perform basic mathematical operations" — executes computational logic based on user-supplied arguments

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

calculator Rate-limited

calculator 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": {
    "calculator": {
      "limits": [
        {
          "counter": "calculator_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 Simple MCP Server, so you can run agents against it safely.

FAQ

Questions about calculator

What does the calculator tool do? +

Perform basic mathematical operations. It is categorised as a Execute tool in the Simple 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 calculator? +

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

What risk level is calculator? +

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

Can I rate-limit calculator? +

Yes. Add a rate_limit block to the calculator 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 calculator completely? +

Set action: deny in the PolicyLayer policy for calculator. 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 calculator? +

calculator is provided by the Simple MCP Server MCP server (shaleen-wonder-ent/simple-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.