Agent-skills read-only-postgres

Execute read-only SQL queries against PostgreSQL databases. Use when: (1) querying PostgreSQL data, (2) exploring schemas/tables, (3) running SELECT queries for analysis, (4) checking database contents. Supports multiple database connections with descriptions for auto-selection. Blocks all write operations (INSERT, UPDATE, DELETE, DROP, etc.) for safety.

install

source · Clone the upstream repo

git clone https://github.com/jawwadfirdousi/agent-skills

Claude Code · Install into ~/.claude/skills/

T=$(mktemp -d) && git clone --depth=1 https://github.com/jawwadfirdousi/agent-skills "$T" && mkdir -p ~/.claude/skills && cp -r "$T/skills/read-only-postgres" ~/.claude/skills/jawwadfirdousi-agent-skills-read-only-postgres && rm -rf "$T"

manifest: skills/read-only-postgres/SKILL.md

source content

PostgreSQL Read-Only Query Skill

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/read-only-postgres-connections.json

Security: Set file permissions to

since it contains credentials:

chmod 600 connections.json

{
  "databases": [
    {
      "name": "app-db-dev",
      "description": "Primary app database (public schema: users, organizations, orders, order_items, events)",
      "host": "localhost",
      "port": 5432,
      "database": "app_dev",
      "user": "app_user",
      "password": "app_password",
      "sslmode": "disable"
    },
    {
      "name": "app-db-staging",
      "description": "Staging database (same schema as primary app)",
      "host": "localhost",
      "port": 5432,
      "database": "app_staging",
      "user": "app_user",
      "password": "app_password",
      "sslmode": "disable"
    }
  ]
}

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
pii_masking	No	Object mapping table names to arrays of column names to mask

PII Masking

Mask sensitive data in query results by adding a

pii_masking

field to any database config. Middle characters are replaced with

, keeping only the first and last characters visible.

{
  "name": "app-db-dev",
  "host": "localhost",
  "database": "app_dev",
  "user": "readonly",
  "password": "secret",
  "pii_masking": {
    "users": ["email", "phone", "first_name", "last_name"],
    "orders": ["shipping_address"]
  }
}

How it works:

```
john@email.com
```
→
```
j************m
```
```
555-1234
```
→
```
5******4
```
```
Jo
```
→
```
Jo
```
(2 chars or fewer are not masked)

Masking is applied automatically when querying a matching table. A footer note indicates which columns were masked.

Usage

List configured databases

python3 scripts/query.py --list

Query a database

python3 scripts/query.py --db app-db-dev --query "SELECT id, email, created_at FROM users LIMIT 10"

List tables

python3 scripts/query.py --db app-db-dev --tables

Show schema

python3 scripts/query.py --db app-db-dev --schema

Limit results

python3 scripts/query.py --db app-db-dev --query "SELECT id, status, total_amount FROM orders" --limit 100

Database Selection

Match user intent to database

description

User asks about	Look for description containing
users, accounts	users, accounts
organizations, teams	organizations, teams
orders, payments	orders, payments
events, audit logs	events, audit, logs
analytics or reporting	analytics, reporting
background jobs or queues	jobs, queue, outbox

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 (comments/literals stripped; DDL/DML keywords, data-modifying CTEs, SELECT INTO, and sequence mutation functions blocked)
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
PII masking: Configurable per-table column masking to protect sensitive data in query output

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