# sqldb-mcp-server

A **read-only** [Model Context Protocol (MCP)](https://modelcontextprotocol.io/) 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
- **Markdown evidence export** – save SQL and query results as a Markdown report file for test evidence
- **Six MCP tools**: `query`, `listTables`, `describeTable`, `explainQuery`, `exportQuery`, `saveQueryEvidence`

## Installation

### From npm (recommended)

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

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

### From source

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

## Quick Start

```bash
# 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`):

```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.

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

Response format (compact / token-efficient):
```json
{
  "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.

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

### `describeTable`

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

```json
{ "table": "dbo.users" }
```

### `explainQuery`

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

```json
{ "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.

```json
{
  "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:
```json
{
  "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.
 
### `saveQueryEvidence`
 
Execute a SELECT query and save the SQL plus the returned rows as a Markdown report file for test evidence.
 
```json
{
  "sql": "SELECT id, name FROM users LIMIT 10",
  "filepath": "/tmp/query-evidence.md"
}
```
 
Response format:
```json
{
  "filepath": "/tmp/query-evidence.md",
  "rowCount": 10,
  "previewRows": [
    { "id": 1, "name": "Alice" },
    { "id": 2, "name": "Bob" }
  ]
}
```
 
If an error occurs, the tool returns the error message text instead of a success payload.
 
## Development

```bash
# 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
```