Northwind PostgreSQL MCP Server

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describe_table

Retrieve column metadata for a PostgreSQL table—names, data types, nullability, defaults, and primary-key status—to inspect schema before writing queries.

Instructions

Return column metadata for a table: name, data type, nullable, default, and whether it is part of the primary key.

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_name": "<table_name>"
    },
    "name": "describe_table"
  }
}

Input Schema

Name	Required	Description	Default
`table_name`	Yes

Output Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Nov 9, 2026

TDQS

B3/5.0

Behavior3/5

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

With no annotations, the description carries the full behavioral burden; it implicitly conveys a read-only lookup and the output schema covers the return shape, but it says nothing about behavior for a nonexistent or unauthorized table, nor whether identifiers need qualification.

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

Conciseness4/5

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

A single front-loaded sentence with a tight enumerated field list; nothing is wasted. It could be marginally improved by adding a routing clause rather than by trimming anything.

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

Completeness3/5

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

The tool is simple and the output schema already documents the return values, so the description is largely sufficient for invocation. It remains incomplete on the one input parameter and on how it relates to the overlapping get_schema sibling.

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

Parameters2/5

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

Schema description coverage is 0%, so the description should compensate for the single table_name parameter, but it never mentions it. It does not clarify whether the name must be exact, qualified by schema/database, or case-sensitive, leaving the only param under-specified.

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

Purpose4/5

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

The description uses a specific verb ('Return') and resource ('column metadata for a table') and enumerates the exact fields returned (name, data type, nullable, default, primary key membership). It does not, however, distinguish itself from the sibling get_schema, which plausibly overlaps, so an agent must open both to decide.

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

Usage Guidelines2/5

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

There is no when-to-use guidance, no mention of when not to use it, and no reference to alternatives such as get_schema, list_tables, or sample_table. The agent is left to infer that this is the per-table metadata call rather than a full-schema dump.

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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