PostgreSQL Read-Only Query Skill

When to Use

Use when querying PostgreSQL databases and access must stay strictly read-only
Use when exploring schemas, tables, and data across multiple configured connections
Use when you want defense-in-depth protection against accidental INSERT/UPDATE/DELETE or DDL

Execute safe, read-only queries against configured PostgreSQL databases.

Requirements

Python 3.8+
psycopg2-binary: pip install -r requirements.txt

Setup

Create connections.json in the skill directory or ~/.config/claude/postgres-connections.json.

Security: Set file permissions to 600 since it contains credentials:

chmod 600 connections.json

{
  "databases": [
    {
      "name": "production",
      "description": "Main app database - users, orders, transactions",
      "host": "db.example.com",
      "port": 5432,
      "database": "app_prod",
      "user": "readonly_user",
      "password": "your-password",
      "sslmode": "require"
    }
  ]
}

Config Fields

Field	Required	Description
name	Yes	Identifier for the database (case-insensitive)
description	Yes	What data this database contains (used for auto-selection)
host	Yes	Database hostname
port	No	Port number (default: 5432)
database	Yes	Database name
user	Yes	Username
password	Yes	Password
sslmode	No	SSL mode: disable, allow, prefer (default), require, verify-ca, verify-full

Usage

List configured databases

python3 scripts/query.py --list

Query a database

python3 scripts/query.py --db production --query "SELECT * FROM users LIMIT 10"

List tables

python3 scripts/query.py --db production --tables

Show schema

python3 scripts/query.py --db production --schema

Limit results

python3 scripts/query.py --db production --query "SELECT * FROM orders" --limit 100

Database Selection

Match user intent to database description:

User asks about	Look for description containing
users, accounts	users, accounts, customers
orders, sales	orders, transactions, sales
analytics, metrics	analytics, metrics, reports
logs, events	logs, events, audit

If unclear, run --list and ask user which database.

Safety Features

Read-only session: Connection uses PostgreSQL readonly=True mode (primary protection)
Query validation: Only SELECT, SHOW, EXPLAIN, WITH queries allowed
Single statement: Multiple statements per query rejected
SSL support: Configurable SSL mode for encrypted connections
Query timeout: 30-second statement timeout enforced
Memory protection: Max 10,000 rows per query to prevent OOM
Column width cap: 100 char max per column for readable output
Credential sanitization: Error messages don't leak passwords

Troubleshooting

Error	Solution
Config not found	Create `connections.json` in skill directory
Authentication failed	Check username/password in config
Connection timeout	Verify host/port, check firewall/VPN
SSL error	Try `"sslmode": "disable"` for local databases
Permission warning	Run `chmod 600 connections.json`

Exit Codes

0: Success
1: Error (config missing, auth failed, invalid query, database error)

Workflow

Run --list to show available databases
Match user intent to database description
Run --tables or --schema to explore structure
Execute query with appropriate LIMIT

Limitations

Read-only protections reduce accidental writes but cannot override database-server policy, triggers, extensions, or an over-privileged account. Use a database role with read-only permissions as the primary control.
Query results can contain personal, confidential, or regulated data. Confirm the intended database and avoid exporting or sharing results without explicit authorization.
The script is not a replacement for backups, auditing, access reviews, or production change controls.

postgres-readonly-queries