mcp-postgres

pg_query

Run parameterized SQL queries with placeholder parameters. Returns query results as JSON rows. Supports safe parameter injection using $1, $2, etc.

Instructions

Execute a parameterized SQL query. Returns rows as JSON. Use $1, $2, ... for parameters.

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": {
      "target": "<target>",
      "sql": "<sql>"
    },
    "name": "pg_query"
  }
}

Input Schema

Name	Required	Description
`sql`	Yes	SQL query with $1, $2, ... placeholders
`params`	No	JSON array of parameter values for placeholders
`target`	Yes	Target name from ~/.dbx/targets/

Schema Changelog

Changes observed during successful MCP inspections.

First observedv2026.4.10-3Jul 25, 2026

TDQS

B3.3/5.0

Behavior2/5

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

No annotations provided. The description only notes return format and parameter syntax, but does not disclose whether the tool can perform destructive actions (e.g., UPDATE, DELETE) or if it is read-only. Lacks safety-relevant behavioral details.

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, zero fluff. All information is front-loaded and every word serves a purpose.

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?

Minimally adequate for a 3-parameter tool with no output schema. Explains purpose and parameters, but lacks context on allowed SQL commands, error behavior, or side effects.

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%, so baseline is 3. The description reinforces the parameter placeholder syntax ($1, $2) but adds limited value beyond the already clear schema descriptions.

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?

Clearly states 'Execute a parameterized SQL query' with verb and resource specificity, and mentions return format (JSON). Distinguishes from sibling tools like pg_query_explain and pg_query_prepared.

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?

Provides no guidance on when to use this tool vs alternatives (e.g., pg_query_explain, pg_insert). Does not state when not to use it, leaving the agent to infer based on name alone.

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