sql-mcp-server

A secure Model Context Protocol (MCP) server that exposes database access to LLM clients via FastMCP.

Supported database providers:

• SQLite
• PostgreSQL
• MySQL
• Microsoft SQL Server (MSSQL)

Features

• Safe-by-default SQL validation middleware
• Read-only mode (DB_READ_ONLY=true) enforced before execution
• Single statement enforcement
• Forbidden keyword detection
• Granular opt-in for destructive statements (e.g. allow DROP via DB_ALLOW_DROP=true)
• Automatic row limiting (LIMIT / TOP)
• Optional table allowlist (DB_ALLOWED_TABLES)
• Multi-instance runtime: expose several databases from a single MCP server
• MCP tools designed for schema exploration and safe querying

Project structure

src/sql_mcp_server/
  main.py
  config.py
  errors.py
  middleware/sql_validator.py
  db/
  tools/

Configuration

Copy .env.example to .env and update values.

Multi-instance setup

Set MCP_INSTANCES to a comma-separated list of prefixes (e.g. MCP_INSTANCES=CRM,ERP). For every prefix, define the expected environment variables by upper-casing the prefix and suffixing standard keys: CRM_DB_PROVIDER, CRM_DB_HOST, etc. Instance identifiers are case-insensitive and available to tools via the instance_id parameter.

When MCP_INSTANCES is omitted, the server exposes a single default instance sourced directly from the un-prefixed environment variables shown below.

SQLite

DB_PROVIDER=sqlite
SQLITE_PATH=./database.db
DB_READ_ONLY=true
DB_MAX_ROWS=100

PostgreSQL

DB_PROVIDER=postgres
DB_HOST=localhost
DB_PORT=5432
DB_USER=myuser
DB_PASSWORD=mypassword
DB_DATABASE=mydb
DB_READ_ONLY=true
DB_MAX_ROWS=100

MySQL

DB_PROVIDER=mysql
DB_HOST=localhost
DB_PORT=3306
DB_USER=myuser
DB_PASSWORD=mypassword
DB_DATABASE=mydb
DB_READ_ONLY=true
DB_MAX_ROWS=100

MSSQL

DB_PROVIDER=mssql
DB_HOST=localhost
DB_PORT=1433
DB_USER=myuser
DB_PASSWORD=mypassword
DB_DATABASE=mydb
DB_READ_ONLY=true
DB_MAX_ROWS=100

ℹ️ The MSSQL client applies DB_QUERY_TIMEOUT via the pyodbc connection timeout when provided; ensure the driver you select supports this property. ⚠️ Make sure to install a SQL Server ODBC driver (e.g., msodbcsql17 / msodbcsql18) before starting the MSSQL instance, otherwise pyodbc cannot establish the connection.

Install

python -m venv .venv
.venv\\Scripts\\activate
pip install -e .

Run

sql-mcp-server

The server runs over stdio (FastMCP default) and can be wired to MCP-compatible clients.

Windsurf configuration (mcp_config.json)

Windsurf can launch this MCP server over stdio. You can configure it in:

~/.codeium/windsurf/mcp_config.json

The examples below use the "module" entrypoint (Option 2):

• command: your venv Python executable
• args: ["-m", "sql_mcp_server.main"]

Common optional env fields

• DB_READ_ONLY (optional, default: true)
• DB_MAX_ROWS (optional, default: 100)
• DB_QUERY_TIMEOUT (optional, default: 10 seconds)
• DB_STATEMENT_TIMEOUT_MS (optional, default: DB_QUERY_TIMEOUT * 1000; caps statement execution time)
• DB_ALLOWED_TABLES (optional, comma-separated allowlist)
• DB_ALLOW_ALTER (optional, default: false; when true, the validator lets ALTER statements pass so you can evolve schemas without fully disabling keyword protection)
• DB_ALLOW_DROP (optional, default: false; set to true only when you intentionally need to run DROP statements)
• ENABLE_QUERY_LOGS (optional, default: false; when enabled, SQL metadata is logged to logs/queries.log with daily rotation)
• LOG_QUERY_BODIES (optional, default: false; when true, full SQL text is logged in addition to the hashed metadata—keep disabled in production)
• SQL_MCP_LOG_LEVEL (optional, default: INFO; override to reduce verbosity in production, e.g. WARNING)
• tokens.txt (project root) stores one username:token:scopes entry per line; scopes accept r, w, a, d.

SQLite (Windsurf)

Required env fields:

• DB_PROVIDER=sqlite
• SQLITE_PATH

{
  "mcpServers": {
    "sql-sqlite": {
      "command": "c:\\dev\\code\\mcp\\sql_mcp_server\\.venv\\Scripts\\python.exe",
      "args": ["-m", "sql_mcp_server.main"],
      "disabled": false,
      "env": {
        "DB_PROVIDER": "sqlite",
        "SQLITE_PATH": "./database.db",
        "DB_READ_ONLY": "true",
        "DB_MAX_ROWS": "100",
        "DB_QUERY_TIMEOUT": "10",
        "DB_ALLOWED_TABLES": ""
      }
    }
  }
}

PostgreSQL (Windsurf)

Required env fields:

• DB_PROVIDER=postgres
• DB_HOST
• DB_PORT (optional, default driver-side; recommended to set)
• DB_USER
• DB_PASSWORD
• DB_DATABASE

{
  "mcpServers": {
    "sql-postgres": {
      "command": "c:\\dev\\code\\mcp\\sql_mcp_server\\.venv\\Scripts\\python.exe",
      "args": ["-m", "sql_mcp_server.main"],
      "disabled": false,
      "env": {
        "DB_PROVIDER": "postgres",
        "DB_HOST": "localhost",
        "DB_PORT": "5432",
        "DB_USER": "myuser",
        "DB_PASSWORD": "mypassword",
        "DB_DATABASE": "mydb",
        "DB_READ_ONLY": "true",
        "DB_MAX_ROWS": "100",
        "DB_QUERY_TIMEOUT": "10",
        "DB_ALLOWED_TABLES": ""
      }
    }
  }
}

MySQL (Windsurf)

Required env fields:

• DB_PROVIDER=mysql
• DB_HOST
• DB_PORT (optional, default driver-side; recommended to set)
• DB_USER
• DB_PASSWORD
• DB_DATABASE

{
  "mcpServers": {
    "sql-mysql": {
      "command": "c:\\dev\\code\\mcp\\sql_mcp_server\\.venv\\Scripts\\python.exe",
      "args": ["-m", "sql_mcp_server.main"],
      "disabled": false,
      "env": {
        "DB_PROVIDER": "mysql",
        "DB_HOST": "localhost",
        "DB_PORT": "3306",
        "DB_USER": "myuser",
        "DB_PASSWORD": "mypassword",
        "DB_DATABASE": "mydb",
        "DB_READ_ONLY": "true",
        "DB_MAX_ROWS": "100",
        "DB_QUERY_TIMEOUT": "10",
        "DB_ALLOWED_TABLES": ""
      }
    }
  }
}

MSSQL (Windsurf)

Required env fields:

• DB_PROVIDER=mssql
• DB_HOST
• DB_USER
• DB_PASSWORD
• DB_DATABASE

Optional env fields:

• DB_PORT (optional; default: 1433)
• DB_MSSQL_ODBC_DRIVER (optional; if unset the server will try: ODBC Driver 18 for SQL Server, then ODBC Driver 17 for SQL Server, then SQL Server)
• DB_MSSQL_TRUST_SERVER_CERTIFICATE (optional; default: false; set to true for local/dev when using a self-signed certificate)

{
  "mcpServers": {
    "sql-mssql": {
      "command": "c:\\dev\\code\\mcp\\sql_mcp_server\\.venv\\Scripts\\python.exe",
      "args": ["-m", "sql_mcp_server.main"],
      "disabled": false,
      "env": {
        "DB_PROVIDER": "mssql",
        "DB_HOST": "localhost",
        "DB_PORT": "1433",
        "DB_USER": "myuser",
        "DB_PASSWORD": "mypassword",
        "DB_DATABASE": "mydb",
        "DB_MSSQL_ODBC_DRIVER": "ODBC Driver 17 for SQL Server",
        "DB_MSSQL_TRUST_SERVER_CERTIFICATE": "true",
        "DB_READ_ONLY": "true",
        "DB_MAX_ROWS": "100",
        "DB_ALLOWED_TABLES": ""
      }
    }
  }
}

MCP tools

• list_tables(instance_id?: str): List accessible tables for the selected instance
• describe_table(table: str, instance_id?: str): Columns for a specific table
• run_select(query: str, instance_id?: str): Execute a validated, safe SELECT query
• run_query(query: str, instance_id?: str): Execute a validated query (write statements allowed when the instance is not read-only)

When embedding the server, call sql_mcp_server.instances.shutdown_instance_registry() during teardown to close database connections cleanly.

Logging & privacy

• Log files live in logs/ and are rotated daily; they are created with 0600 permissions to avoid accidental exposure.
• Query logs store only query length and a SHA-256 hash by default; enable them via ENABLE_QUERY_LOGS=true, then turn on LOG_QUERY_BODIES=true only if you genuinely need the raw SQL for debugging.
• Adjust SQL_MCP_LOG_LEVEL to reduce verbosity in production.

Authentication (API keys)

• Enable authentication by providing a tokens.txt file (by default located at the project root) with one username:token:scopes line per user.
• list_tables and describe_table require the r scope.
• run_select requires r. run_query requires w and will also demand a/d whenever the statement contains ALTER or DROP operations allowed by the instance config.
• Pass the token through the api_key parameter of each MCP tool call (or define API_KEY in the client environment so FastMCP injects it automatically).
• Use python scripts/generate_api_key.py <username> --scopes rwad to append entries to tokens.txt (use --file to target another file or --stdout to print without writing). Remove a user with python scripts/remove_api_key.py <username>.

Security notes

• Always use a database user with the least privileges possible.
• Prefer DB-level read-only privileges in addition to middleware enforcement.

License

MIT