mcp-toolbox-sqlserver

A Claude Code skill that connects Claude directly to your SQL Server database during development, built on Google's MCP Toolbox for Databases.

When building database-backed tools, you constantly need to verify what data is in the database — to confirm test data exists before smoke testing, explore table schemas before writing queries, or debug unexpected results against raw records. This skill removes the PowerShell step: Claude queries the database on your behalf, inline in the conversation where you're already working.

What it does

1. Downloads the toolbox.exe binary if not already present
2. Collects your SQL Server connection details (with sensible defaults)
3. Creates a tools.yaml following a schema-first workflow — discovers real table/column names before writing any queries
4. Registers the MCP server in Claude Code
5. Guides you through VS Code restart and verification
6. Flags known pitfalls so you don't hit them

How to trigger it

Invoke with /mcp-toolbox-sqlserver, or just describe what you want — Claude will pick it up:

# Direct invocation
/mcp-toolbox-sqlserver

# Natural language — all of these trigger the skill:
"setup mcp toolbox for my SQL Server database"
"connect Claude Code to my MSSQL dev database without PowerShell"
"I want to query Umbraco Engage data directly from Claude"
"help me setup database tools for Claude Code, SQL Server on localhost:1433"

Sample onboarding prompts

Use these as starting points. Claude will ask for any missing details.

Security note: Never paste real production passwords into a chat prompt. Use these patterns with dev/local credentials only.

Minimal — just tell it the DB:

setup mcp toolbox for SQL Server, database UmbracoEngageV17_TestSite on localhost

With full credentials (dev environment):

I want to setup mcp toolbox to query my SQL Server database directly from Claude Code.
Server: localhost, port: 1433, database: UmbracoEngageV17_TestSite, user: sa

From a fresh Umbraco Engage clone:

I just cloned the Umbraco Engage repo and got the TestSite running.
I want Claude to be able to check whether reporting tables are populated,
explore the schema before I write queries, and spot-check data while I implement tools.
How do I connect Claude to the database?

Generic project (non-Umbraco):

help me connect Claude Code to my MSSQL dev database so I can query it without writing PowerShell.
SQL Server in a Docker container on localhost:1433, database MyAppDb, user dev

Defaults

Field	Default / Sample
Host	localhost
Port	1433
Database	UmbracoEngageV17_TestSite
User	sa
Password	(required — example: YourPassword@123)
MCP server name	Based on DB name, e.g. myapp_db (underscores only)

Benchmark results (iteration 1, 2026-05-07)

Evaluated against 3 real-world prompts, each run with and without the skill.

Eval	with_skill	without_skill
1 — Umbraco Engage, standard setup	8/8 ✅	4/8
2 — Docker MSSQL, generic project	8/8 ✅	4/8
3 — Umbraco natural language query	8/8 ✅	5/8 ⚠️
Pass rate	100%	48%

Metric	with_skill	without_skill
Avg tokens	30,450	22,126 (+38% overhead)
Avg duration	160s	103s (+55% overhead)

What the skill adds over baseline:

• Correct kind: mssql source type (baseline used cloud-sql-mssql or Docker HTTP mode)
• Schema-first workflow enforced (baseline wrote all tools upfront, guessing table/column names)
• Underscore naming explained explicitly (baseline got it right by accident or missed it)
• Correct claude mcp add flags (baseline used wrong flags or wrong transport)
• encrypt: disable for localhost (baseline often missed this)

Known eval limitation: Eval 3 baseline scored slightly higher (5/8) because the subagent could see the existing toolbox.exe on disk, leaking context. A clean-machine baseline would likely score 3-4/8.

Known pitfalls (encoded in skill)

#	Symptom	Fix
1	MCP tools not visible after setup	Server name has hyphen → rename with underscore, restart VS Code
2	SQL syntax error on alias	Reserved word → wrap with [brackets]
3	"Invalid object name"	Guessed wrong table name → run list_tables first
4	"Invalid column name"	Guessed wrong column → run describe_table first
5	Tools invisible despite Connected status	VS Code not restarted → close and reopen
6	Port 5000 conflict in logs	HTTP mode conflict, harmless in stdio mode → ignore
7	TLS/certificate error	Missing encrypt: disable in source config

Files

umbraco-mcp-toolbox/
├── SKILL.md       ← skill instructions (read by Claude)
├── README.md      ← this file
└── evals/
    └── evals.json ← benchmark test cases