Compare execution plans of two queries with cost analysis
AI agents call query_plan_compare 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 plan comparison and cost analysis, which is a read/analytical operation. It inspects execution plans (EXPLAIN output) rather than running queries that modify data. The risk is low since it only retrieves metadata about query plans.
From the tool's definition 'Compare execution plans of two queries with cost analysis' — reads and analyzes query plans without executing the queries or modifying data
Documented attack patterns abuse exactly the kind of access query_plan_compare 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 query_plan_compare:
{
"version": "1",
"default": "deny",
"tools": {
"query_plan_compare": {}
}
}query_plan_compare is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Compare execution plans of two queries with cost analysis. 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 query_plan_compare: 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.
query_plan_compare 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 query_plan_compare 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 query_plan_compare. 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.
query_plan_compare 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.
Free to start. No card required.
60 Postgres Mcp Legacy tools catalogued and risk-classified — across an index of 43,000+ MCP servers.