List all constraints for a table (PK, FK, UNIQUE, CHECK).
AI agents call list_constraints 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 queries database metadata about constraints (PK, FK, UNIQUE, CHECK) on a specified table. It retrieves information without altering data, executing code, or triggering external operations. The blast radius of misuse is minimal; an agent could learn table structure but cannot modify, delete, or execute arbitrary operations. Classification as Read is appropriate.
From the tool's definition Tool description states it 'List[s] all constraints for a table' — a retrieval operation with no modification or execution of side effects. Aligns with sibling read-only tools like describe_table, list_tables, list_schemas, and list_indexes.
Documented attack patterns abuse exactly the kind of access list_constraints 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 list_constraints:
{
"version": "1",
"default": "deny",
"tools": {
"list_constraints": {}
}
}list_constraints is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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List all constraints for a table (PK, FK, UNIQUE, CHECK). 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 list_constraints: 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.
list_constraints 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 list_constraints 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 list_constraints. 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.
list_constraints 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.