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

1. Run --list to show available databases
2. Match user intent to database description
3. Run --tables or --schema to explore structure
4. 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.