SqlAugur

SqlAugur

An MCP server that gives AI assistants safe, read-only access to SQL Server databases. Every query is parsed into a full AST using Microsoft's official T-SQL parser — not regex — so comment injection, string literal tricks, and encoding bypasses are blocked at the syntax level.

┌──────────────┐          ┌───────────────────────────────────────────┐        ┌──────────────┐
│              │  stdio   │  SqlAugur                                 │        │              │
│  AI Client   │◄────────►│                                           │───────►│  SQL Server  │
│              │          │  ┌────────────┐  ┌──────────────────────┐ │        │              │
└──────────────┘          │  │  Query     │  │  Schema / Diagram /  │ │        └──────────────┘
                          │  │  Validator │  │  DBA Services        │ │
                          │  └────────────┘  └──────────────────────┘ │
                          │  ┌────────────────────────────────────┐   │
                          │  │  Rate Limiter                      │   │
                          │  └────────────────────────────────────┘   │
                          └───────────────────────────────────────────┘

Quick Start

Prerequisite: .NET 10.0 runtime

1. Install

dotnet tool install -g SqlAugur

2. Configure — create ~/.config/sqlaugur/appsettings.json (Linux/macOS) or %APPDATA%\sqlaugur\appsettings.json (Windows), setting the connection string for your environment:

{
  "SqlAugur": {
    "Servers": {
      "production": {
        "ConnectionString": "Server=myserver;Database=master;Integrated Security=True;TrustServerCertificate=False;Encrypt=True;"
      }
    }
  }
}

3. Connect — add to your MCP client:

Add to your Claude Desktop config (claude_desktop_config.json):

{
  "mcpServers": {
    "sqlaugur": {
      "command": "sqlaugur"
    }
  }
}

claude mcp add --transport stdio sqlaugur -- sqlaugur

Or add to .mcp.json in your project root:

{
  "mcpServers": {
    "sqlaugur": {
      "type": "stdio",
      "command": "sqlaugur"
    }
  }
}

Add to .vscode/mcp.json in your workspace:

{
  "servers": {
    "sqlaugur": {
      "command": "sqlaugur"
    }
  }
}

4. Verify — ask your AI assistant to list_servers and you should see your configured connection.

For Docker, Podman, and other install methods, see Installation.

Why This Approach

• AST-level query validation — Most MCP database servers use keyword blocking or no validation at all. This project parses every query into a full syntax tree using Microsoft's official TSql170Parser. Comment injection, string literal tricks, and encoding bypasses are blocked at the syntax level, not with fragile regex patterns.

• Rate limiting — Token bucket throughput limiting and concurrency control prevent runaway AI query loops from overwhelming production SQL Servers. No other MCP database server offers this.

• DBA diagnostic tooling — Integrated support for First Responder Kit, DarlingData, and sp_WhoIsActive with parameter blocking that prevents write operations. This is an entirely new MCP capability category.

• Progressive discovery — Up to 29 tools organized into toolsets that load on demand. Only 6 core tools are exposed initially, keeping the AI's context window small and reducing token usage. Additional toolsets are discovered and enabled as needed.

Features

Security

• Read-only by design — only SELECT and CTE queries are permitted
• AST-based query validation using ScriptDom (not regex)
• Parameter blocking on all diagnostic stored procedures to prevent writes
• Concurrency and throughput rate limiting

Database Tooling

• Multi-server support — named connections to multiple SQL Server instances
• Schema overview — concise Markdown schema maps with PKs, FKs, constraints, and defaults
• Table documentation — Markdown descriptions of columns, indexes, foreign keys, and constraints
• ER diagram generation — PlantUML and Mermaid diagrams with smart cardinality detection
• Schema exploration — list programmable objects, view definitions, extended properties, dependency graphs
• Query plan analysis — estimated or actual XML execution plans
• DBA diagnostics — optional integration with First Responder Kit, DarlingData, and sp_WhoIsActive
• Progressive discovery — dynamic toolset mode reduces initial context window usage by exposing tools on demand

Installation

All methods produce the same MCP server.

NuGet Global Tool (recommended)

Prerequisite: .NET 10.0 runtime

dotnet tool install -g SqlAugur

Create your configuration file:

# Linux/macOS
mkdir -p ~/.config/sqlaugur
# Edit ~/.config/sqlaugur/appsettings.json with your server connections

# Windows (PowerShell)
mkdir "$env:APPDATA\sqlaugur" -Force
# Edit %APPDATA%\sqlaugur\appsettings.json with your server connections

MCP client configuration:

{
  "mcpServers": {
    "sqlserver": {
      "command": "sqlaugur"
    }
  }
}

To update: dotnet tool update -g SqlAugur

Docker / Podman

# Volume-mount a config file
docker run -i --rm \
  -v /path/to/appsettings.json:/app/appsettings.json:ro,Z \
  ghcr.io/mbentham/sqlaugur:latest

# Or use environment variables (no config file needed)
docker run -i --rm \
  -e SqlAugur__Servers__production__ConnectionString="Server=host.docker.internal;Database=master;..." \
  ghcr.io/mbentham/sqlaugur:latest

Note: To reach a SQL Server on the host machine, use host.docker.internal (Docker Desktop) or --network=host (Linux). Replace docker with podman — all commands are identical. The :Z flag on volume mounts is required for SELinux-enabled systems (Fedora, RHEL); Docker Desktop users on macOS/Windows can omit it.

MCP client configuration:

{
  "mcpServers": {
    "sqlserver": {
      "command": "docker",
      "args": ["run", "-i", "--rm",
        "-v", "/path/to/appsettings.json:/app/appsettings.json:ro,Z",
        "ghcr.io/mbentham/sqlaugur:latest"]
    }
  }
}

services:
  sqlaugur:
    image: ghcr.io/mbentham/sqlaugur:latest
    stdin_open: true
    volumes:
      - ./appsettings.json:/app/appsettings.json:ro,Z

MCP client configuration:

{
  "mcpServers": {
    "sqlserver": {
      "command": "docker",
      "args": ["compose", "run", "-i", "--rm", "sqlaugur"]
    }
  }
}

Build from Source

Prerequisite: .NET 10.0 SDK

git clone [email protected]:mbentham/SqlAugur.git
cd SqlAugur
dotnet publish SqlAugur -c Release -o SqlAugur/publish
cp SqlAugur/appsettings.example.json SqlAugur/publish/appsettings.json
# Edit SqlAugur/publish/appsettings.json with your server connections

MCP client configuration:

{
  "mcpServers": {
    "sqlserver": {
      "command": "dotnet",
      "args": ["/absolute/path/to/SqlAugur/publish/SqlAugur.dll"]
    }
  }
}

Configuration

The server loads configuration from multiple sources. Higher-priority sources override lower ones:

1. Command-line arguments
2. Environment variables — using __ as section delimiter (e.g., SqlAugur__Servers__production__ConnectionString=...)
3. Current working directory — appsettings.json in the directory you run the command from
4. User config directory — ~/.config/sqlaugur/appsettings.json on Linux, %APPDATA%\sqlaugur\appsettings.json on Windows
5. Azure Key Vault — when AzureKeyVaultUri is set (see below)
6. App directory — appsettings.json next to the DLL

Example configuration (Windows Authentication — recommended):

{
  "SqlAugur": {
    "Servers": {
      "production": {
        "ConnectionString": "Server=myserver;Database=master;Integrated Security=True;TrustServerCertificate=False;Encrypt=True;"
      }
    },
    "MaxRows": 1000,
    "CommandTimeoutSeconds": 30,
    "MaxConcurrentQueries": 5,
    "MaxQueriesPerMinute": 60,
    "EnableFirstResponderKit": false,
    "EnableDarlingData": false,
    "EnableWhoIsActive": false,
    "EnableDynamicToolsets": false
  }
}

Security Note: appsettings.json is gitignored to prevent accidental credential commits. See SECURITY.md for recommended authentication methods including Windows Authentication, Azure Managed Identity, and secure credential storage options.

Tools

The server provides 29 tools organized into toolsets. Six core tools are always available. Additional toolsets are loaded at startup (static mode) or on demand (dynamic mode).

Core Tools

DBA Diagnostic Tools

Each toolkit is enabled independently via config flags and requires the corresponding stored procedures installed on the target SQL Server.

Install from: github.com/BrentOzarULTD/SQL-Server-First-Responder-Kit

Install from: github.com/erikdarling/DarlingData

Install from: whoisactive.com

Progressive Discovery

When EnableDynamicToolsets is true, only core tools load at startup. Three meta-tools let the AI discover and enable additional toolsets on demand, reducing initial context window usage:

Example flow:

1. AI calls list_toolsets — sees first_responder_kit is "available" (configured but not yet enabled)
2. AI calls get_toolset_tools("first_responder_kit") — reviews the 6 tools and their parameters
3. AI calls enable_toolset("first_responder_kit") — the 6 tools are now registered and usable
4. AI calls sp_blitz — runs the health check as normal

In static mode (EnableDynamicToolsets: false), all enabled toolsets load at startup and the discovery tools are not registered. Schema Exploration and Diagrams toolsets are always loaded regardless of mode.

Known limitation: Progressive discovery relies on the MCP notifications/tools/list_changed notification to inform clients that new tools have been registered. Claude Code does not currently handle this notification (anthropics/claude-code#4118), so dynamically enabled toolsets will not appear. Use static mode (EnableDynamicToolsets: false) when using Claude Code.

Security

Query Validation

Every query is parsed into an Abstract Syntax Tree (AST) using Microsoft's official TSql170Parser and must pass these rules:

• Single statement only — multiple statements are rejected
• SELECT only — INSERT, UPDATE, DELETE, DROP, EXEC, CREATE, ALTER, and all other statement types are blocked
• No SELECT INTO — prevents table creation via SELECT
• No external data access — OPENROWSET, OPENQUERY, OPENDATASOURCE, OPENXML blocked
• No linked servers — four-part name references are rejected
• No MAXRECURSION hint — prevents overriding the default recursion limit
• Cross-database queries are allowed — three-part names work by design; the security boundary is the server, not the database. To restrict to a single database, limit the login's permissions.

Because validation operates on the parsed AST, it correctly handles edge cases that defeat string-based approaches: keywords inside comments, string literals, nested block comments, and encoding tricks.

Parameter Blocking

Diagnostic stored procedures execute via whitelisted procedure names with blocked parameters that prevent writes:

• First Responder Kit — all @Output* parameters blocked (prevents writing results to server tables)
• DarlingData — logging and output parameters blocked (prevents table creation and data retention)
• sp_WhoIsActive — @destination_table, @return_schema, @schema, @help blocked

Rate Limiting

All tool executions are subject to concurrency limiting (MaxConcurrentQueries, default 5) and throughput limiting (MaxQueriesPerMinute, default 60). Excess requests are rejected with a retry message.

Connection Security

Use Windows Authentication or Azure Managed Identity where possible to avoid storing credentials in config files. When SQL Authentication is required, use environment variable overrides to inject credentials at runtime. See SECURITY.md for detailed guidance including credential stores and connection string encryption.

Known Risks

• This project depends on the official Microsoft MCP C# SDK (ModelContextProtocol NuGet package) which is currently a prerelease version. Prerelease packages may contain undiscovered security vulnerabilities and receive breaking changes. As the MCP framework handles all protocol I/O, any vulnerability in it directly affects this application's security boundary. Monitor the package for stable releases and upgrade when available.
• The data returned from a SQL Server query could include malicious prompt injection targeting AIs. This is a risk of all AI use and cannot be mitigated by this project. Ensure you're following best practices for AI security and only connecting to trusted data sources.

Contributing

Contributions are welcome. See CONTRIBUTING.md for architecture details, development setup, testing instructions, and guidelines for adding new tools.

License

MIT