sqldb-mcp-server

A read-only Model Context Protocol (MCP) server that exposes SQL database access to LLMs.

Features

• Multi-database – supports MSSQL, PostgreSQL, and MySQL
• Read-only – only SELECT statements are allowed (enforced via AST-level SQL parsing with the correct dialect per DB type)
• LLM-optimised – results use a compact columnar format (column list + value rows) to reduce token usage
• Pagination – skip / take parameters with automatic cap at 100 rows
• Total-count aware – every query result includes meta.totalCount so the LLM knows how many rows exist
• Caching – query / schema results are cached with a configurable TTL
• File export – stream query results to CSV or JSON files without a row-count limit
• Five MCP tools: query, listTables, describeTable, explainQuery, exportQuery

Installation

From npm (recommended)

# Install globally
npm install -g @akrym1582/sqldb-mcp-server

# Or run directly with npx (no install needed)
npx @akrym1582/sqldb-mcp-server

From source

git clone https://github.com/akrym1582/sqldb-mcp-server.git
cd sqldb-mcp-server
npm install
npm run build

Quick Start

# 1. Install globally
npm install -g @akrym1582/sqldb-mcp-server

# 2. Configure environment variables (see below)
export DB_TYPE=postgresql
export DB_HOST=localhost
export DB_USER=myuser
export DB_PASSWORD=mypassword
export DB_NAME=mydb

# 3. Run
sqldb-mcp-server

Or use in your MCP client configuration (e.g. Claude Desktop claude_desktop_config.json):

{
  "mcpServers": {
    "sqldb": {
      "command": "npx",
      "args": ["-y", "@akrym1582/sqldb-mcp-server"],
      "env": {
        "DB_TYPE": "postgresql",
        "DB_HOST": "localhost",
        "DB_PORT": "5432",
        "DB_USER": "myuser",
        "DB_PASSWORD": "mypassword",
        "DB_NAME": "mydb"
      }
    }
  }
}

Environment Variables

Variable	Default	Description
DB_TYPE	mssql	Database type: mssql, postgresql, or mysql
DB_HOST	–	Database server hostname
DB_PORT	1433 / 5432 / 3306	Database server port (default depends on DB_TYPE)
DB_USER	–	Database username
DB_PASSWORD	–	Database password
DB_NAME	–	Database name
DB_ENCRYPT	true for MSSQL/PostgreSQL, false for MySQL	Enables encrypted DB connections. MSSQL trusts the server certificate. PostgreSQL tries SSL first and falls back to plain if SSL is unavailable. MySQL uses TLS with certificate verification disabled when enabled.
DB_QUERY_TIMEOUT	30000	Query timeout in milliseconds (used by query / explainQuery)
EXPORT_QUERY_TIMEOUT	300000	Export query timeout in milliseconds (used by exportQuery; default 5 min)
CACHE_TTL	60	Cache TTL in seconds

Default ports by DB type

DB_TYPE	Default DB_PORT
mssql	1433
postgresql	5432
mysql	3306

MCP Tools

query

Execute a SELECT SQL statement.

{
  "sql": "SELECT id, name FROM users WHERE active = 1",
  "skip": 0,
  "take": 10
}

Response format (compact / token-efficient):

{
  "meta": { "totalCount": 42, "returnedCount": 10, "skip": 0, "take": 10 },
  "columns": ["id", "name"],
  "rows": [[1, "Alice"], [2, "Bob"], ...]
}

listTables

List all base tables in the database.

[{ "schema": "dbo", "name": "users" }, ...]

describeTable

Describe a table's columns, indexes, foreign keys, check constraints, and size statistics.

{ "table": "dbo.users" }

explainQuery

Return the estimated execution plan for a SELECT query without executing it.

{ "sql": "SELECT * FROM orders WHERE status = 'open'" }

exportQuery

Stream a SELECT query result to a file. Designed for large datasets – there is no row-count limit and results are written directly to disk using Node.js streams.

{
  "sql": "SELECT * FROM large_table",
  "filepath": "/tmp/export.csv",
  "format": "csv",
  "options": { "delimiter": ",", "bom": false }
}

format defaults to "csv" if omitted. "json" is also supported.

CSV options (all optional):

Option	Default	Description
delimiter	","	Column separator
nullValue	""	String to write for NULL / undefined cells
bom	false	Prepend UTF-8 BOM (useful for Excel)

JSON options (all optional):

Option	Default	Description
pretty	false	Indent the output JSON

Response format:

{
  "filepath": "/tmp/export.csv",
  "format": "csv",
  "rowCount": 50000
}

The tool uses a separate, longer-lived connection pool whose requestTimeout is controlled by EXPORT_QUERY_TIMEOUT (default 300 000 ms = 5 min). Increase this value for very large exports.

Development

# Clone the repository
git clone https://github.com/akrym1582/sqldb-mcp-server.git
cd sqldb-mcp-server

# Install dependencies
npm install

# Configure environment
cp .env.example .env
# Edit .env with your DB credentials

# Run in dev mode (no compile step)
npm run dev

# Or build and run
npm run build
npm start

# Run unit tests
npm test

Project Structure

src/
  mcp/
    server.ts           # MCP server entry point
    tools/
      query.ts          # query tool
      listTables.ts     # listTables tool
      describeTable.ts  # describeTable tool
      explainQuery.ts   # explainQuery tool
      exportQuery.ts    # exportQuery tool (streaming file export)
  db/
    index.ts            # DB adapter factory (selects adapter from DB_TYPE)
    types.ts            # DB interfaces (including queryStream)
    adapters/
      mssql.ts          # Microsoft SQL Server implementation
      postgresql.ts     # PostgreSQL implementation (pg + pg-cursor)
      mysql.ts          # MySQL implementation (mysql2)
  utils/
    row-result.ts       # Compact columnar result format
    sanitize.ts         # AST-based SQL read-only validation (dialect-aware)
    pagination.ts       # skip/take normalisation
    cache.ts            # TTL in-memory cache
    export-writer.ts    # Streaming CSV / JSON file writer
  __tests__/            # Unit tests