query_db · Demo MCP: Risk & Policy

WHAT IT DOES

What query_db does on Demo

AI agents invoke query_db to trigger actions in Demo. 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 query_db needs a policy

Although described as read-only SELECT queries, this tool executes SQL against a local database. The enforcement of read-only behavior depends on implementation (e.g., whether it uses a read-only connection or just trusts the query text). If an attacker can inject arbitrary SQL, DDL/DML could run.

From the tool's definition 'Run a read-only SELECT query against local SQLite demo.db' — executes SQL queries against a database

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

query_db Rate-limited

query_db 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": {
    "query_db": {
      "limits": [
        {
          "counter": "query_db_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 Demo, so you can run agents against it safely.

FAQ

Questions about query_db

What does the query_db tool do? +

Run a read-only SELECT query against local SQLite demo.db. It is categorised as a Execute tool in the Demo MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on query_db? +

Register the Demo MCP server in PolicyLayer and add a rule for query_db: 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 Demo. Nothing to install.

What risk level is query_db? +

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

Can I rate-limit query_db? +

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

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

query_db is provided by the Demo MCP server (penguinszp001/mcp-server-demo). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.