AI agents call query to retrieve information from PostgreSQL without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
Even though query only reads data, uncontrolled read access leaks sensitive information and racks up API costs — an agent caught in a retry loop can make thousands of calls a minute without anyone noticing.
Documented attack patterns abuse exactly the kind of access query gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and PostgreSQL, and nothing reaches the server without passing your rules. This is the rule we recommend for query:
{
"version": "1",
"default": "deny",
"tools": {
"query": {}
}
}query is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Run a read-only SQL query. It is categorised as a Read tool in the PostgreSQL MCP Server, which means it retrieves data without modifying state.
Register the PostgreSQL MCP server in PolicyLayer and add a rule for 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 PostgreSQL. Nothing to install.
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 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 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.
query is provided by the PostgreSQL MCP server (@modelcontextprotocol/server-postgres). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 1 PostgreSQL tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
1 PostgreSQL tool catalogued and risk-classified — across an index of 42,500+ MCP servers.