postgres-readonly-queries – Writing & Content skill for AI agents

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": "verify-full"
    }
  ]
}

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, verify-full (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: Conservative keyword/semicolon checks, not a SQL parser or authorization boundary
• Single statement: Multiple statements per query rejected
• SSL support: Configurable SSL mode for encrypted connections
• Query timeout: 30-second statement timeout enforced
• Display cap: At most 10,000 rows printed; the client/server may still buffer or compute a much larger result
• 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 | Check certificate hostname, root CA and server TLS configuration; do not disable verification to bypass errors |

| 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.

Use bash only for shell examples and python3 scripts/query.py for the inert helper. Keep credential config outside version control, restrict file permissions before adding credentials, and never print values. --limit caps displayed rows without rewriting SQL; include a reviewed SQL LIMIT for server-side work where appropriate. Keyword/semicolon checks reject some valid SQL and cannot prevent SELECT function side effects, external calls or all temporary writes. Read-only privileges and a trusted, restricted function environment are essential. EXPLAIN ANALYZE actually executes its query. Python buffering and large individual values can still exhaust memory; use a dedicated bounded reporting query.