PostgreSQL MCP Server

List Installed PostgreSQL Extensions

pg_list_extensions

Read-onlyIdempotent

Retrieve a list of all extensions currently installed in a PostgreSQL database, including version and description, formatted as JSON or Markdown.

Instructions

List all extensions currently installed in the PostgreSQL database.

Returns extension name, installed version, default version, and description.

Returns: JSON: { extensions: ExtensionInfo[], count: number } Markdown: formatted table

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "pg_list_extensions"
  }
}

Input Schema

Name	Required	Description	Default
`response_format`	No	Output format: 'markdown' for human-readable, 'json' for machine-readable	markdown

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Jun 18, 2026

TDQS

A4.3/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true, destructiveHint=false, and idempotentHint=true, so the description doesn't need to restate those. However, it adds useful details about the return format (JSON/Markdown) and the fields included (name, installed version, etc.), which enhances transparency beyond the schema.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is three sentences long, front-loaded with the action ('List all extensions'), and efficiently conveys the return format and fields. Every sentence serves a purpose without unnecessary verbosity.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's low complexity (1 optional parameter, no output schema), the description is complete. It explains the output format and content, and the parameter is already well-documented in the schema. No additional information is needed for an agent to use this tool correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, with the single parameter 'response_format' fully described (enum, default, description). The description does not add additional semantics beyond what the schema provides, so baseline score of 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states 'List all extensions currently installed in the PostgreSQL database' with a specific verb and resource. It distinguishes itself from sibling tools (e.g., pg_list_tables, pg_list_databases) by focusing on extensions, leaving no ambiguity about what it does.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description makes it clear that this tool is for listing extensions, which is straightforward given the tool name and title. While it does not explicitly state when to avoid using it or name alternative tools, the context of sibling tools provides sufficient differentiation for an agent to select the correct tool.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.