list_distinct_values

THE RISK

Low Risk

Why list_distinct_values needs a policy

This tool retrieves and lists unique values from captured traffic data without modifying, deleting, or executing anything. It is a read-only operation similar to a list or search function. The low severity reflects that discovering available endpoints or field values in already-captured traffic data poses minimal risk even if misused by an agent, as it cannot modify systems or execute operations.

From the tool's definition Tool description states 'List unique values for a field, ordered by frequency' and the server context describes 'search, analyze, and debug application API traffic' with no mention of modification, deletion, or execution capabilities.

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

POLICY

How to control list_distinct_values

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

policy.json

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

list_distinct_values 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 Tusk Drift MCP — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

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EXPLORE

Related tools and policies

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All 6 Tusk Drift MCP tools →

Read tools on other servers

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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 list_distinct_values

What does the list_distinct_values tool do? +

List unique values for a field, ordered by frequency. Use this tool to: - Discover available endpoints (field:. It is categorised as a Read tool in the Tusk Drift MCP MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on list_distinct_values? +

Register the Tusk Drift MCP server in PolicyLayer and add a rule for list_distinct_values: 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 Tusk Drift MCP. Nothing to install.

What risk level is list_distinct_values? +

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

Can I rate-limit list_distinct_values? +

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

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

list_distinct_values is provided by the Tusk Drift MCP server (use-tusk/drift-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Tusk Drift MCP tool call.

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

CHECK YOUR STACK →