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MCPg - Production-grade PostgreSQL MCP Server

MCPg - Production-grade PostgreSQL MCP Server

by devopam
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Hybrid

Export query

export_query
Read-only

Run a read-only SQL query and serialize its rows to CSV or JSON, flagging limit-based truncation so callers can paginate results.

Instructions

Run a read-only SQL query and serialise its rows to CSV or JSON. Reuses the SQL-safety checks of run_select. Truncates at limit rows and flags it in the result so callers can paginate.

Example: export_query(sql='SELECT id, email FROM users', format='csv', limit=10000)

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": "export_query"
  }
}

Input Schema

NameRequiredDescriptionDefault
sqlYes
limitNo
formatNocsv
databaseNoOptional: a database id from list_databases, to target a configured secondary (read-only) database; omit for the primary. Database names that are not configured ids are rejected.

Output Schema

NameRequiredDescriptionDefault
formatYes
contentYes
row_countYes
truncatedYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv0.8.4
    • changedInput schema / properties / database / description
      Previous value: -"Optional: target a configured secondary (read-only) database by name; omit for the primary. Call list_databases to see the configured ids."New value: +"Optional: a database id from list_databases, to target a configured secondary (read-only) database; omit for the primary. Database names that are not configured ids are rejected."
  2. First observedv0.6.8

TDQS

A3.9/5.0
Behavior4/5

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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the bar is lower, yet the description still adds real behavior: read-only enforcement, reuse of run_select's safety checks, hard truncation at `limit`, and a truncation flag that enables caller-side pagination. It does not clarify whether output is returned inline rather than written to a file path, which is the one ambiguity left.

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?

Three tight sentences front-load the core behavior and the example is genuinely useful for call shape. No filler, though the example largely restates parameter names already covered in the schema.

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-value detail is not required, and the description covers safety, formatting, and truncation well. The remaining gap is whether 'export' means inline payload versus a file destination, which matters for a tool with this name.

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 only 25% (only `database` is documented), so the description must compensate; it does explain `limit` (truncation threshold) and `format` (CSV or JSON) plus a worked example with concrete values. However, it never states whether limit=0 means unlimited, whether format accepts only 'csv'/'json' case-sensitively, or that sql must be a single SELECT.

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 gives a specific verb (run + serialise) plus resource (SQL query rows) and names the output formats (CSV or JSON). Saying it 'reuses the SQL-safety checks of run_select' anchors it against the closest sibling, so an agent can distinguish it from a plain query tool without reading the schema.

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?

Mentioning run_select implies the family relationship, and the limit/pagination note hints at bulk use, but there is no explicit 'use this when you need exportable output instead of run_select' or 'use export_table for whole tables' routing. The agent must infer when to prefer this over run_select or export_table.

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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