VS Code Copilot Configuration¶

This guide explains how to configure VS Code with GitHub Copilot to use the RIDDL MCP Server for AI-assisted domain modeling.

Prerequisites¶

Visual Studio Code installed
GitHub Copilot and Copilot Chat extensions installed and activated
riddlg installed and on your PATH (see Installation):
```
brew install ossuminc/tap/riddlg
```

Configuration¶

VS Code has built-in MCP support. Define the server once and Copilot's agent mode can use it. The simplest scope is per-workspace, in .vscode/mcp.json.

Workspace Configuration¶

Create .vscode/mcp.json in your project root:

{
  "servers": {
    "riddl": {
      "type": "stdio",
      "command": "riddlg",
      "args": ["mcp"]
    }
  }
}

VS Code launches riddlg mcp as a local process — no URL and no API key. After saving, VS Code shows a Start action above the server entry; click it (or reload the window) to bring the tools online.

User-Level Configuration¶

To make the server available in every workspace, add an mcp block to your user settings.json (open with Cmd+Shift+P → "Preferences: Open User Settings (JSON)"):

{
  "mcp": {
    "servers": {
      "riddl": {
        "type": "stdio",
        "command": "riddlg",
        "args": ["mcp"]
      }
    }
  }
}

riddlg must be found on PATH

If the tools don't appear, use the absolute path (e.g. /opt/homebrew/bin/riddlg) as the command.

Verify Connection¶

Open Copilot Chat (Cmd+Shift+I or Ctrl+Shift+I) and switch to Agent mode
Ask: "Can you validate this RIDDL code?" and paste some RIDDL
Copilot should invoke the riddl_validate tool

You can see and toggle the available tools with the Tools picker in the Chat view.

Using with RIDDL Files¶

For the best experience, install both:

GitHub Copilot - AI assistance with MCP tools
RIDDL Language Support - Syntax highlighting and local validation

This gives you real-time highlighting and local validation as you type, plus AI-powered assistance via Copilot Chat.

Usage Examples¶

Validate the Open File¶

Validate the RIDDL file I have open and explain any errors

Check Model Completeness¶

What's missing from my domain model in this folder?

Generate RIDDL from a Description¶

Create a RIDDL context for managing customer subscriptions with monthly billing, plan changes, and cancellation

Fix Errors¶

I'm getting "Undefined reference to type OrderId" - how do I fix this?

Troubleshooting¶

MCP Not Recognized¶

Verify the Copilot Chat extension is installed and you're in Agent mode
Reload the window after editing .vscode/mcp.json or settings
Check the Output panel → "MCP" for startup logs

Server Won't Start¶

Verify riddlg mcp runs from a terminal (it waits on stdin)
If riddlg isn't found, use its absolute path as command
Confirm riddlg version works

Available RIDDL Tools¶

Tool	Use For
`riddl_validate`	Check RIDDL source for errors
`riddl_outline`	Summarize a model's definitions
`validate-partial`	Check incomplete models
`check-completeness`	Find missing elements
`check-simulability`	Verify simulation readiness
`map-domain-to-riddl`	Convert descriptions to RIDDL
`explain-error`	Understand validation errors
`suggest-next`	Get recommendations

See MCP Tools for the full catalog of 13.

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