Get the execution plan for a SQL query (EXPLAIN).
AI agents call explain_query to retrieve information from Postgres without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
EXPLAIN queries databases to retrieve optimization metadata and execution plans. This is a passive retrieval operation with no side effects, data modification, or code execution. It aligns with the Read category (retrieves or queries data; no side effects). Severity is low because misuse cannot corrupt data, trigger financial transactions, or delete records — it can only expose schema information via query plans.
From the tool's definition Tool name 'explain_query' and description 'Get the execution plan for a SQL query (EXPLAIN)' — EXPLAIN is a read-only SQL command that returns query metadata without executing or modifying data.
Documented attack patterns abuse exactly the kind of access explain_query gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Postgres, and nothing reaches the server without passing your rules. This is the rule we recommend for explain_query:
{
"version": "1",
"default": "deny",
"tools": {
"explain_query": {}
}
}explain_query is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Get the execution plan for a SQL query (EXPLAIN). It is categorised as a Read tool in the Postgres MCP Server, which means it retrieves data without modifying state.
Register the Postgres MCP server in PolicyLayer and add a rule for explain_query: 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 Postgres. Nothing to install.
explain_query is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the explain_query 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.
Set action: deny in the PolicyLayer policy for explain_query. 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.
explain_query is provided by the Postgres MCP server (javimaligno/postgres_mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Postgres, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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14 Postgres tools catalogued and risk-classified — across an index of 43,000+ MCP servers.