PostgreSQL Python MCP Server

中文文档 | English

A Python-based PostgreSQL MCP server providing secure database operations with built-in safety checks and AST-based SQL parsing.

Features

• 🔍 Database Listing: List all databases in the PostgreSQL instance

• 📋 Table Listing: View all tables in the configured database

• 🔍 Table Description: Detailed table structure information

• 📊 Safe Querying: Execute SQL queries (SELECT only by default)

• 🛡️ Security Boundaries: Strict operation limits within configured database

• ⚙️ Configurable: Support for enabling additional operations via environment variables

• 📋 JSON Output: Structured JSON responses optimized for AI consumption

• 🌳 AST-Based Security: Advanced SQL parsing using Abstract Syntax Trees for 100% accuracy

Related MCP server: postgresql-mcp

Security Features

Default Safe Mode

• Only allows SELECT, SHOW, DESCRIBE, EXPLAIN queries

• Blocks all WITH statements because they can wrap write operations

• Blocks dangerous operations like DROP, DELETE, UPDATE, INSERT

• Strictly limits operations to the configured database scope

• Prevents SQL injection attacks using AST-based analysis

• Detects nested dangerous operations and UNION-based attacks

Advanced Mode (Optional)

Set environment variable PG_ALLOW_DANGEROUS=true to enable:

• Full CRUD operations

• Extended database management functions

Configuration

Environment Variables

Claude Desktop Configuration Example

Add to your Claude Desktop configuration file:

{
  "mcpServers": {
    "postgresql": {
      "command": "uvx",
      "args": [
        "--from",
        "git+https://github.com/hexonal/pg-python-mcp-.git",
        "pg-python-mcp"
      ],
      "env": {
        "PG_HOST": "your-postgres-host:5432",
        "PG_USER": "your-username",
        "PG_PASSWORD": "your-password",
        "PG_DATABASE": "your-database"
      }
    }
  }
}

Available Tools

1. list_databases

Lists all databases in the PostgreSQL instance (current configured database is highlighted).

2. list_tables

Lists all tables in the currently configured database.

3. describe_table

Describes the structure of a specified table, including column names, types, null constraints, and key information.

Parameters:

• table_name (string): Name of the table to describe

4. execute_query

Executes SQL query statements and returns results in JSON format.

Parameters:

• query (string): SQL statement to execute

Security Constraints:

• Default mode only allows query operations (SELECT, SHOW, DESCRIBE, EXPLAIN)

• WITH statements are always rejected in safe mode

• Automatically detects and blocks dangerous operations using AST parsing

• Operations limited to the configured database scope

• 100% accuracy in detecting SQL injection attempts

JSON Output Format:

{
  "status": "success",
  "message": "Query executed successfully, returned 2 rows",
  "columns": ["id", "name", "email"],
  "data": [
    {
      "id": 1,
      "name": "User 1", 
      "email": "user1@example.com"
    },
    {
      "id": 2,
      "name": "User 2",
      "email": "user2@example.com"
    }
  ]
}

Installation and Usage

Using uvx (Recommended)

# Install from Git
uvx --from git+https://github.com/hexonal/pg-python-mcp-.git pg-python-mcp

# Or for local development
uvx pg-python-mcp

Manual Installation

# Clone repository
git clone https://github.com/hexonal/pg-python-mcp-.git
cd pg-python-mcp

# Install dependencies
pip install -e .

# Run server
python -m pg_mcp

Usage Examples

List All Databases

Tool: list_databases

List Tables in Current Database

Tool: list_tables

Describe Table Structure

Tool: describe_table
Parameters: {"table_name": "users"}

Execute Query

Tool: execute_query  
Parameters: {"query": "SELECT * FROM users LIMIT 10"}

Development

Project Structure

pg-python-mcp/
├── pg_mcp/
│   ├── __init__.py          # Main MCP server entry point
│   ├── __main__.py          # Run script
│   └── pg_handler.py        # PostgreSQL handler with AST security
├── test_ast_security.py     # AST security validation tests
├── test_stdio.py           # MCP protocol testing
├── pyproject.toml          # Project configuration
├── README.md               # English documentation
└── README_zh.md            # Chinese documentation

Local Development

# Clone project
git clone https://github.com/hexonal/pg-python-mcp-.git
cd pg-python-mcp

# Install development dependencies
pip install -e ".[dev]"

# Run security tests
python test_ast_security.py

# Test MCP protocol
python test_stdio.py

# Code formatting
black pg_mcp/
isort pg_mcp/

# Type checking
mypy pg_mcp/

Technology Stack

• FastMCP 2.0: Modern MCP framework with decorator-based tool registration

• asyncpg: Async PostgreSQL database operations

• sqlparse: SQL Abstract Syntax Tree parsing for security analysis

• Python 3.8+: Broad compatibility support

Security Implementation

AST-Based SQL Analysis

The server uses Abstract Syntax Tree parsing to achieve 100% accuracy in SQL security checking:

def is_query_safe(self, query: str) -> tuple[bool, str]:
    """Check query safety using AST parsing"""
    try:
        parsed = sqlparse.parse(query)
        for statement in parsed:
            is_safe, error_msg = self._check_statement_safety(statement)
            if not is_safe:
                return False, error_msg
        return True, ""

Security Test Results

• ✅ Safe queries: 8/8 (100%)

• 🛡️ Dangerous queries blocked: 10/10 (100%)

• 🎯 Overall accuracy: 100%

License

MIT License

Security Notice

⚠️ Important Security Guidelines:

• All environment variables are required with no unsafe defaults

• Ensure minimal PostgreSQL user permissions in production

• Regularly rotate database passwords

• Avoid using administrative database users in configuration

• Run this MCP server in isolated environments

• Default safe mode provides basic protection but cannot replace comprehensive security policies

Troubleshooting

Common Issues

1. Connection Failed: Check if PostgreSQL service is running and network connectivity

2. Environment Variable Error: Verify all required environment variables are properly set

3. Permission Error: Confirm PostgreSQL user has access permissions to the specified database

4. Query Rejected: Check if query contains forbidden keywords, or consider enabling advanced mode

5. MCP Protocol Issues: Ensure you're using FastMCP 2.0 compatible configuration

Getting Help

• Check the Chinese documentation for additional details

• Review the test files for usage examples

• Examine the AST security tests for supported query patterns