explainQuery · Postgresql MCP: Risk & Policy

WHAT IT DOES

What explainQuery does on Postgresql

AI agents invoke explainQuery to trigger actions in Postgresql. 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 explainQuery needs a policy

While EXPLAIN alone is a read-only operation, EXPLAIN ANALYZE actually executes the underlying SQL query. If the query contains side-effecting statements (e.g., INSERT, UPDATE, DELETE), those effects will materialize. This makes the tool capable of execution with real side effects, warranting the Execute category.

From the tool's definition 'Optionally run EXPLAIN ANALYZE to get actual execution statistics (this executes the query)'

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

explainQuery Rate-limited

explainQuery 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": {
    "explainQuery": {
      "limits": [
        {
          "counter": "explainquery_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 Postgresql, so you can run agents against it safely.

FAQ

Questions about explainQuery

What does the explainQuery tool do? +

Get the execution plan for a SQL query using EXPLAIN. Optionally run EXPLAIN ANALYZE to get actual execution statistics (this executes the query). Useful for optimizing query performance and understanding how PostgreSQL processes your queries. It is categorised as a Execute tool in the Postgresql MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on explainQuery? +

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

What risk level is explainQuery? +

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

Can I rate-limit explainQuery? +

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

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

explainQuery is provided by the Postgresql MCP server (vnikhilbuddhavarapu/postgresql-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.