describe_available_tools

THE RISK

Low Risk

Why describe_available_tools needs a policy

The tool queries available capabilities and returns suggestions based on user input. It performs no calculations, modifies no state, executes no external operations, and creates no financial commitments. It is purely informational—analogous to a help or list command. The low severity reflects that misuse would only expose metadata about available tools, not cause unintended calculations or financial transactions.

From the tool's definition Tool name 'describe_available_tools' and description indicate it 'Find[s] the right tool for your math or finance problem' and provides 'tool suggestions' in response to natural language queries.

Documented attack patterns abuse exactly the kind of access describe_available_tools gives an agent:

POLICY

How to control describe_available_tools

PolicyLayer is an MCP gateway — it sits between your AI agents and MCP Calc Tools, and nothing reaches the server without passing your rules. This is the rule we recommend for describe_available_tools:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "describe_available_tools": {}
  }
}

describe_available_tools is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.

Create a free account and register MCP Calc Tools — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

CAP THIS TOOL →

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EXPLORE

Related tools and policies

More MCP Calc Tools tools

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Data exfiltration → How read access becomes an exfiltration channel when chained with untrusted content.
MCP token cost → What connecting this server costs in context-window tokens on every request.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about describe_available_tools

What does the describe_available_tools tool do? +

Find the right tool for your math or finance problem. Describe your goal in natural language and get tool suggestions. Examples: describe_available_tools(. It is categorised as a Read tool in the MCP Calc Tools MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on describe_available_tools? +

Register the MCP Calc Tools MCP server in PolicyLayer and add a rule for describe_available_tools: 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 MCP Calc Tools. Nothing to install.

What risk level is describe_available_tools? +

describe_available_tools is a Read tool with low risk. Read-only tools are generally safe to allow by default.

Can I rate-limit describe_available_tools? +

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

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

describe_available_tools is provided by the MCP Calc Tools MCP server (nbiish/mcp-calc-tools). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every MCP Calc Tools tool call.

Start from MCP Calc Tools, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →