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mcp-postgres-guard

mcp-postgres-guard

by vladshykanov
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Remote

Describe table

describe_table
Read-onlyIdempotent

View table schema including column types, nullability, and defaults, with masked columns indicated to protect sensitive data.

Instructions

Columns, types, nullability and defaults for one table. Masked columns are marked — they can be filtered on, but their values are never returned.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "table": "<table>"
    },
    "name": "describe_table"
  }
}

Input Schema

NameRequiredDescriptionDefault
tableYesTable name, optionally schema-qualified (e.g. public.users)

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A4/5.0
Behavior4/5

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

Annotations already declare readOnlyHint and idempotentHint. The description adds that masked columns are marked and can be filtered but never returned, which is useful behavioral context 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?

Two sentences with no wasted words. The first sentence states the core purpose, the second adds an important detail about masked columns.

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?

The description is complete for a simple schema inspection tool: it explains what is returned (columns, types, nullability, defaults, masked marks) given one parameter. However, it could mention the return format (list of columns) explicitly.

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 description coverage is 100%, so the schema already documents the parameter. The description does not add new information beyond what the schema provides (table name, optionally schema-qualified).

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 the tool returns columns, types, nullability, and defaults for a single table, which matches the tool name and distinguishes it from siblings like list_tables (lists tables) and query (runs queries).

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

Usage Guidelines3/5

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

The description implies the tool is for inspecting table schema, but it does not explicitly state when to use it over siblings like list_tables or query, nor does it provide when-not-to-use 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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