Agent Skills: PostgreSQL

PostgreSQL

A CLI tool for exploring and debugging PostgreSQL databases with JSON-first output designed for AI agents.

CLI Discovery

The CLI is located at ./pgtool-cli/ relative to this SKILL.md file.

| Platform | Script | | ---------------- | ------------------------------------------ | | Unix/Linux/macOS | pgtool | | Windows | pgtool.cmd (pgtool.ps1 also available) |

For setup instructions, see SETUP.md in this directory.

Important

• Always use pgtool-cli for all database operations. Do NOT use psql directly.
• If pgtool-cli encounters an error or limitation, report the issue to the user and stop. Do not fall back to psql or other tools.
• Always add LIMIT to SELECT queries to avoid fetching excessive data.
• Protected profiles require human approval via a GUI dialog. If you receive a PROTECTED_DENIED error, ask the user to approve the connection dialog on their screen, then retry.
• Read-only profiles will reject write operations. Check the profile's readOnly flag before attempting writes.

Global Options

pgtool <command> [OPTIONS]

Options come after the command name (citty framework requirement):

| Option | Description | |--------|-------------| | -r, --root <path> | Project root directory (default: auto-detect) | | --plain | Human-readable output instead of JSON | | -p, --profile <name> | Connection profile name | | --read-only | Force read-only mode | | --allow-writes | Override read-only profile |

# ✅ Correct — options after command
pgtool schemas -p dev
pgtool tables --profile staging --plain

# ❌ Wrong — options before command don't work
pgtool -p dev schemas

Profile selection priority: --profile flag > PGTOOL_PROFILE env > config "default" > first profile.

Commands

List Profiles

pgtool profiles

Output: {"ok":true,"profiles":[{"name":"dev","host":"localhost","port":5432,"database":"myapp_dev","default":true,"readOnly":false,"protected":false}]}

List Schemas

pgtool schemas
pgtool -p staging schemas

Output: {"ok":true,"schemas":[{"name":"public","owner":"postgres"}]}

List Tables

# Tables in default schema
pgtool tables

# Tables in a specific schema with specific profile
pgtool -p staging tables auth

Output: {"ok":true,"schema":"public","tables":[{"name":"users","type":"table","rowEstimate":1000,"sizeHuman":"256 KB"}]}

Describe Table

Get column details with primary key and foreign key information.

pgtool describe users
pgtool describe auth.users

Output includes column types, nullability, defaults, PK/FK info, and foreign key references.

List Indexes

pgtool indexes users

Output: {"ok":true,"indexes":[{"name":"users_pkey","unique":true,"primary":true,"columns":["id"],"type":"btree"}]}

List Constraints

pgtool constraints users

Output includes PRIMARY KEY, FOREIGN KEY, UNIQUE, CHECK, and EXCLUDE constraints.

List Relationships

Get all foreign key relationships in a schema.

pgtool relationships
pgtool relationships auth

Output: {"ok":true,"relationships":[{"fromTable":"orders","fromColumns":["user_id"],"toTable":"users","toColumns":["id"]}]}

Execute Query

pgtool query "SELECT * FROM users WHERE active = true LIMIT 100"

Output: {"ok":true,"rows":[...],"rowCount":5,"fields":["id","name","email"]}

Best Practices:

• Always add LIMIT to SELECT queries to avoid fetching excessive data
• DML statements (INSERT, UPDATE, DELETE) with RETURNING are fully supported
• Use parameterized values in WHERE clauses to avoid SQL injection

Sample Table Rows

pgtool sample users
pgtool sample users --limit 10
pgtool sample auth.users

Output: {"ok":true,"schema":"public","table":"users","rows":[...],"rowCount":5,"columns":["id","name","email"]}

Count Table Rows

pgtool count users

Output: {"ok":true,"schema":"public","table":"users","count":12345}

Search Tables and Columns

pgtool search email

Output: {"ok":true,"pattern":"email","matches":{"tables":[...],"columns":[...]}}

Schema Overview

pgtool overview
pgtool overview auth

Compact ERD-like view showing tables, primary keys, and relationships.

Explain Query Plan

pgtool explain "SELECT * FROM users WHERE email = 'x'"
pgtool explain "SELECT * FROM users WHERE id = 1" --no-analyze

Output: {"ok":true,"query":"SELECT...","plan":["Seq Scan on users..."]}

Daemon Management

pgtool daemon start    # Start or confirm daemon is running
pgtool daemon stop     # Gracefully stop daemon
pgtool daemon status   # Show status, uptime, active pools

The daemon auto-starts on the first CLI call and auto-stops after 5 minutes idle. It maintains persistent connection pools across CLI calls for faster queries.

Error Responses

All errors return JSON with ok: false, an error code, and a helpful hint:

{
  "ok": false,
  "error": "Configuration file not found",
  "code": "CONFIG_NOT_FOUND",
  "hint": "Create a .pgtool.json file..."
}

| Code | Description | |------|-------------| | CONFIG_NOT_FOUND | .pgtool.json not found | | CONFIG_INVALID | Invalid config format or missing fields | | CONFIG_INSECURE | .pgtool.json has insecure (writable) file permissions | | CONFIG_TAMPERED | Config modified while daemon running, change rejected | | CONNECTION_FAILED | Cannot connect to database | | QUERY_FAILED | SQL error | | TABLE_NOT_FOUND | Table does not exist | | SCHEMA_NOT_FOUND | Schema does not exist | | PERMISSION_DENIED | Auth failed or insufficient privileges | | TIMEOUT | Query timed out | | READ_ONLY | Write blocked on read-only connection | | PROTECTED_DENIED | Protected profile not approved by human |

Handling PROTECTED_DENIED

If you receive this error, it means the profile requires human approval. Ask the user to approve the connection — a dialog will appear on their screen. Then retry the command.

Handling CONFIG_INSECURE

The .pgtool.json file has write permissions, which is a security risk since it contains database credentials. Ask the user to make it read-only by running chmod 400 .pgtool.json in their project directory, then retry.

Handling READ_ONLY

The profile or --read-only flag prevents write operations. Use a different profile or ask the user to adjust the config.

Common Usage Patterns

Exploring a new database:

1. pgtool profiles - See available connection profiles
2. pgtool -p dev schemas - See available schemas
3. pgtool overview - Quick view of tables and relationships
4. pgtool tables <schema> - List tables with sizes
5. pgtool describe <table> - Understand table structures
6. pgtool sample <table> - See example data

Finding data:

1. pgtool search <pattern> - Find tables/columns by name
2. pgtool sample <table> - Quick data preview
3. pgtool count <table> - Get exact row count
4. pgtool query "SELECT..." - Custom queries

Debugging data issues:

1. pgtool describe <table> - Verify column types
2. pgtool sample <table> - Check actual data
3. pgtool explain "SELECT..." - Analyze query performance
4. pgtool indexes <table> - Check index coverage

Understanding relationships:

1. pgtool overview - Visual relationship map
2. pgtool relationships - Get all FK relationships
3. pgtool constraints <table> - See specific table constraints

Working with multiple environments:

1. pgtool profiles - List all available profiles
2. pgtool -p dev tables - Explore dev database
3. pgtool -p staging tables - Compare with staging
4. pgtool -p prod tables - Access prod (will prompt for approval if protected)