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@yawlabs/postgres-mcp

by YawLabs
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TypeScript
Remote

List roles

pg_list_roles
Read-onlyIdempotent

List database roles with login, superuser, createdb, createrole attributes and inherited memberships to identify who has access to a database.

Instructions

List database roles (users and groups) with their login/superuser/createdb/createrole attributes and inherited role memberships. Use this to answer 'who has access to this database?' without needing to read pg_authid directly.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
includeSystemNoIf true, include built-in `pg_*` roles (pg_read_all_data, pg_monitor, etc.).

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
rowsYes

Schema Changelog

Changes observed during successful MCP inspections. Dates show when Glama detected each change.

  1. Changed2 schema fields changedv0.12.0
    • changedInput schema / $schema
      Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"
    • changedOutput schema / (root)
      Previous value: -nullNew value: +{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "additionalProperties": false,
+  "properties": {
+    "rows": {
+      "items": {
+        "additionalProperties": false,
+        "properties": {
+          "bypass_rls": {
+            "type": "boolean"
+          },
+          "can_login": {
+            "description": "False for a group role.",
+            "type": "boolean"
+          },
+          "createdb": {
+            "type": "boolean"
+          },
+          "createrole": {
+            "type": "boolean"
+          },
+          "member_of": {
+            "description": "Roles this one is a direct member of; empty when none.",
+            "items": {
+              "type": "string"
+            },
+            "type": "array"
+          },
+          "name": {
+            "type": "string"
+          },
+          "replication": {
+            "type": "boolean"
+          },
+          "superuser": {
+            "type": "boolean"
+          }
+        },
+        "required": [
+          "name",
+          "can_login",
+          "superuser",
+          "createdb",
+          "createrole",
+          "replication",
+          "bypass_rls",
+          "member_of"
+        ],
+        "type": "object"
+      },
+      "type": "array"
+    }
+  },
+  "required": [
+    "rows"
+  ],
+  "type": "object"
+}
  2. First observedv0.7.0

TDQS

A4/5.0
Behavior3/5

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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds useful content detail (attributes and inherited memberships) and notes it reads pg_authid indirectly, but does not disclose auth requirements, error behavior, or other operational traits.

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?

Two focused sentences: the first states exactly what is listed, the second gives the motivating use case. No filler or restatement of the title.

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

Completeness4/5

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

For a one-optional-parameter listing tool with annotations and an output schema, the description is nearly complete. It could marginally strengthen the 'access' framing by noting that this returns role-level principals rather than object-level privileges, but the core information is sufficient.

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%: the includeSystem parameter already has a clear description in the schema. The main description does not discuss parameters, so it adds no meaning beyond the schema, matching the baseline.

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?

Opens with a specific verb and direct object: 'List database roles (users and groups)' and enumerates the exact attributes returned. The mention of answering 'who has access to this database?' and avoiding pg_authid clearly frames what this tool is for and separates it from table/view/function inspection siblings.

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 gives a concrete use case ('Use this to answer "who has access to this database?"') but does not explicitly state when not to use it or name an alternative sibling. It is clear context without exclusionary guidance.

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

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