Explains the execution plan for a SQL query, showing how the database will execute it and provides detailed cost estimates.
AI agents call explain_query to retrieve information from Postgres Mcp Legacy without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool performs a query analysis operation that returns metadata about how a SQL query would be executed. It has no side effects: it does not modify data, delete data, execute the actual query against the database, or trigger external operations.
From the tool's definition Tool name is 'explain_query' and description states it 'Explains the execution plan for a SQL query, showing how the database will execute it and provides detailed cost estimates.' The EXPLAIN operation in PostgreSQL is a read-only diagnostic tool that does…
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 Mcp Legacy, 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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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 Legacy MCP Server, which means it retrieves data without modifying state.
Register the Postgres Mcp Legacy 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 Mcp Legacy. 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 Legacy MCP server (neverinfamous/postgres-mcp-legacy). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Postgres Mcp Legacy, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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60 Postgres Mcp Legacy tools catalogued and risk-classified — across an index of 43,000+ MCP servers.