AI agents call list_extensions to retrieve information from PostgREST without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves information about database extensions without modifying, deleting, or executing operations. It is purely informational, making it a Read operation with minimal blast radius if misused by an AI agent.
From the tool's definition Tool name 'list_extensions' and description 'Lists all extensions in the database' indicate a query/retrieval operation with no side effects.
Documented attack patterns abuse exactly the kind of access list_extensions gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and PostgREST, and nothing reaches the server without passing your rules. This is the rule we recommend for list_extensions:
{
"version": "1",
"default": "deny",
"tools": {
"list_extensions": {}
}
}list_extensions is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Lists all extensions in the database. It is categorised as a Read tool in the PostgREST MCP Server, which means it retrieves data without modifying state.
Register the PostgREST MCP server in PolicyLayer and add a rule for list_extensions: 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 PostgREST. Nothing to install.
list_extensions 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_extensions 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_extensions. 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_extensions is provided by the PostgREST MCP server (supabase/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 32 PostgREST tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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32 PostgREST tools catalogued and risk-classified — across an index of 42,500+ MCP servers.