pg-insight-mcp

Explain query

explain_query

Read-onlyIdempotent

Show the PostgreSQL execution plan for a read-only query without running it.

Instructions

Show the PostgreSQL execution plan for a read-only query without running it.

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": {
      "sql": "<sql>"
    },
    "name": "explain_query"
  }
}

Input Schema

Name	Required	Description	Default
`sql`	Yes

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Nov 5, 2026

TDQS

A3.7/5.0

Behavior4/5

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

Annotations already declare readOnlyHint and idempotentHint, so the safety bar is low, yet the description still contributes real behavior: no execution occurs, so no side effects or data changes. It leaves open what happens if a non-read-only statement is passed (error vs. rejection).

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 no filler; the key constraint (no execution) lands immediately. It is efficient, though slightly terse for the responsibilities it carries.

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?

An output schema exists so return values need no explanation, and the tool is simple with one parameter. The core gaps are edge-case handling for non-SELECT input and the absence of any pointer to run_query or the schema-inspection siblings.

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?

Only one parameter exists and the schema has 0% description coverage, so the description carries the load. It implies sql must be a read-only statement, but says nothing about multi-statement input, placeholders, or whether EXPLAIN ANALYZE behavior is ever triggered.

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?

Names a specific verb and resource ("Show the PostgreSQL execution plan") and adds a scoping constraint ("read-only query, without running it"). It is clearly distinguishable from run_query by the non-execution guarantee, though it never names the sibling explicitly.

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 read-only/without-running qualifiers imply this is a pre-flight inspection step before run_query, but the description never states when to prefer it over run_query or what to do if the query is a write. Usage must be inferred rather than read.

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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