mssql — Claude Code skill: what it does, how to install

---
name: mssql
description: "Execute read-only SQL queries against multiple Microsoft SQL Server databases. Use when: (1) querying MSSQL/SQL Server databases, (2) exploring database schemas/tables, (3) running SELECT queries for data analysis, (4) checking database contents. Supports multiple database connections with descriptions for intelligent auto-selection. Blocks all write operations (INSERT, UPDATE, DELETE, DROP, etc.) for safety."
license: Apache-2.0
metadata:
  author: sanjay3290
  version: "1.0"
---

# MSSQL Read-Only Query Skill

Execute safe, read-only queries against configured Microsoft SQL Server databases.

## Requirements

- Python 3.8+
- pymssql: `pip install -r requirements.txt`

## Setup

Create `connections.json` in the skill directory or `~/.config/claude/mssql-connections.json`.

**Security**: Set file permissions to `600` since it contains credentials:
```bash
chmod 600 connections.json
```

```json
{
  "databases": [
    {
      "name": "production",
      "description": "Main app database - users, orders, transactions",
      "host": "db.example.com",
      "port": 1433,
      "database": "app_prod",
      "user": "readonly_user",
      "password": "your-password",
      "encrypt": true,
      "tds_version": "7.3"
    }
  ]
}
```

### Config Fields

| Field | Required | Description |
|-------|----------|-------------|
| name | Yes | Identifier for the database (case-insensitive) |
| description | Yes | What data this database contains (used for auto-selection) |
| host | Yes | Database hostname |
| port | No | Port number (default: 1433) |
| database | Yes | Database name |
| user | Yes | Username |
| password | Yes | Password |
| encrypt | No | Enable TLS encryption (default: false) |
| tds_version | No | TDS protocol version: 7.0, 7.1, 7.2, 7.3, 7.4 (default: auto) |

## Usage

### List configured databases
```bash
python3 scripts/query.py --list
```

### Query a database
```bash
python3 scripts/query.py --db production --query "SELECT TOP 10 * FROM users"
```

### List tables
```bash
python3 scripts/query.py --db production --tables
```

### Show schema
```bash
python3 scripts/query.py --db production --schema
```

### Limit results
```bash
python3 scripts/query.py --db production --query "SELECT * FROM orders" --limit 100
```

**Note**: MSSQL uses `TOP N` instead of `LIMIT`. The `--limit` flag automatically inserts `TOP N` after SELECT.

## Database Selection

Match user intent to database `description`:

| User asks about | Look for description containing |
|-----------------|--------------------------------|
| users, accounts | users, accounts, customers |
| orders, sales | orders, transactions, sales |
| analytics, metrics | analytics, metrics, reports |
| logs, events | logs, events, audit |

If unclear, run `--list` and ask user which database.

## Safety Features

- **Read-only enforcement**: Query validation blocks write operations (use a `db_datareader` role user for server-side protection)
- **Query validation**: Only SELECT, SHOW, EXPLAIN, WITH, SP_HELP queries allowed
- **Single statement**: Multiple statements per query rejected
- **TLS support**: Configurable encryption for secure connections
- **Query timeout**: 30-second timeout enforced via pymssql
- **Connection timeout**: 10-second login timeout
- **Memory protection**: Max 10,000 rows per query to prevent OOM
- **Column width cap**: 100 char max per column for readable output
- **Credential sanitization**: Error messages don't leak passwords

## Troubleshooting

| Error | Solution |
|-------|----------|
| Config not found | Create `connections.json` in skill directory |
| Authentication failed | Check username/password in config |
| Connection timeout | Verify host/port, check firewall/VPN |
| TDS version error | Try `"tds_version": "7.3"` or `"7.4"` |
| Encryption error | Set `"encrypt": true` for Azure SQL |
| Permission warning | Run `chmod 600 connections.json` |

## Exit Codes

- **0**: Success
- **1**: Error (config missing, auth failed, invalid query, database error)

## Workflow

1. Run `--list` to show available databases
2. Match user intent to database description
3. Run `--tables` or `--schema` to explore structure
4. Execute query with appropriate `--limit` (auto-converts to TOP N)