Avalonia Devtools MCP

Avalonia DevTools MCP

Use this skill when the task involves validating or debugging runtime UI behavior in a running Avalonia app, especially when visual inspection, tree traversal, property/style inspection, or screenshots are needed.

When to use

• "Show me the visual tree"
• "Find this control in the running app"
• "What styles/properties are applied at runtime?"
• "Take a screenshot of this panel/window"
• "Simulate click/text input and verify result"

Preconditions

1. DevTools MCP server configured in user MCP config (for VS Code in this environment):
   • ~/Library/Application Support/Code/User/mcp.json
2. Tool installed:
   • dotnet tool install --global AvaloniaUI.DeveloperTools
3. App instrumentation in target app:
   • AvaloniaUI.DiagnosticsSupport package
   • .WithDeveloperTools() or this.AttachDeveloperTools() at startup
   • Keep this instrumentation development-only (Debug), since MCP enables live inspection, mutation, and input simulation.

Standard workflow

1. attach-to-app with no id
2. If multiple/any clients returned, select one and call attach-to-app with that id
3. Inspect with:
   • tree (roots/subtree)
   • search (type/x:Name)
   • props, styles, resources
   • screenshot
4. Interact with:
   • input, action, set-prop, pseudo-class
5. detach when done

Important pitfalls

• Do not tell users to press F12 for MCP connectivity. F12 opens standalone tools and does not establish MCP attach by itself.
• attach-to-app commonly returns an app list first; a second call with selected id is expected.
• Node IDs are ephemeral; reacquire via tree/search after UI changes.

License/auth caveat observed in this repo

In this environment, forcing AVALONIA_TOOLS_LICENSE_KEY through MCP server env could produce:

Authenticated session does not have access to required product: avalonia-developer-tools-console

Working behavior was restored by removing explicit MCP env override and relying on an already-authenticated DevTools session.

If license/product errors appear:

1. Ensure AvaloniaUI.DeveloperTools is current:
   • dotnet tool update --global AvaloniaUI.DeveloperTools
   • If not installed yet: dotnet tool install --global AvaloniaUI.DeveloperTools
2. Verify license key and entitlement for DevTools MCP.
3. For the exact observed error above (and when a cached authenticated session is available), try removing explicit MCP env override for AVALONIA_TOOLS_LICENSE_KEY, then retry attach.
4. If a portal sign-in dialog appears, ask the user to complete it (do not enter credentials from the agent).