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.
This tool retrieves query execution plan information and cost estimates. It performs no data modification, deletion, or external side effects. EXPLAIN in PostgreSQL is explicitly safe and non-destructive—it shows how a query *would* be executed but does not actually run it against data. This is a classic Read operation: inspection and metadata retrieval with no side effects.
From the tool's definition Tool name 'explain_query' and description 'Explains the execution plan for a SQL query, showing how the database will execute it and provides detailed cost estimates.' — the EXPLAIN command in PostgreSQL is a read-only operation that analyzes and returns…
Attacks that exploit this kind of access
Explains the execution plan for a SQL query, showing how the database will execute it and provides detailed cost estimates. 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 (mirenqinggege/postgres-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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