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chncaesar

pg-semantic-mcp

by chncaesar

sample_data

Retrieve sample rows from any PostgreSQL table to quickly inspect data structure and content. Specify schema.table and optional row limit for efficient previews.

Instructions

Return sample rows from a table.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
limitNoNumber of rows to return. Defaults to SAMPLE_DATA_LIMIT env var (default 5).
tableYesTable name in "schema.table" format or bare table name.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
resultYes
Behavior3/5

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

With no annotations, the description carries the full burden. It conveys the core behavior of returning a sample of rows, implying a limited result set, but does not disclose details like ordering, randomness, or error handling. This is adequate for a simple read tool but lacks richness.

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 a single, front-loaded sentence with no filler. It is extremely concise and to the point.

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 low-complexity tool with two well-documented parameters and an output schema present, the short description covers the essentials. Minor improvements like adding use-case context would help, but it's generally complete.

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 descriptions cover both parameters fully, including table format and limit default behavior. The description adds no additional parameter context, so the baseline 3 applies given high schema coverage.

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's action (return), object (sample rows), and target (a table). It distinguishes itself from siblings like list_tables (metadata) and describe_table (schema) by focusing on data rows.

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 provides no explicit guidance on when to use this tool versus alternatives. Usage is implied by the name and description, but there is no direct statement such as 'Use for previewing data' or exclusions for other tools.

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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