DevTools MCP Server times out connecting to app (avdt 2.2.0-beta2, Avalonia 11.2.0, Windows)

[anose001]

What I'm trying to do:

Connect the Avalonia DevTools MCP server to my running Avalonia app via Claude Code CLI and Jetbrains Codex AI Assistant. The goal is to inspect the visual tree and interact with the UI through the MCP protocol. I am on the Avalonia Accelerate 30-day Business free trial.

Environment:

• Windows 11 (Build 26200.7623)

• .NET 10.0 (net10.0-windows, win-x64)

• Avalonia 11.2.0

• AvaloniaUI.DiagnosticsSupport 2.2.0-beta2 (NuGet, referenced in shared project)

• avdt global tool 2.2.0-beta2

• Avalonia Accelerate 30-day Business free trial

License key situation:

The MCP docs state that ACCELERATE_LICENSE_KEY must be set. However, in the Accelerate portal we only see a license key for UI components (format: avln_on_key:v1:...). We do not see a separate dedicated key for DevTools/MCP. We used the UI components key as ACCELERATE_LICENSE_KEY since it's the only key available in the portal. It's unclear if this is the correct key or if MCP requires a different one that isn't available on the 30-day Business trial.

Setup:

• AvaloniaUI.DiagnosticsSupport package installed in the shared project (Artsy.csproj)

• Old Avalonia.Diagnostics package is not installed

• App.axaml.cs calls this.AttachDeveloperTools() inside #if DEBUG in Initialize()

• App is built and run in Debug configuration

• MCP server configured in .ai/mcp/mcp.json:

"avalonia_devtools": {

"command": "avdt",

"args": ["mcp"],

"env": {

"ACCELERATE_LICENSE_KEY": "avln_on_key:v1:..."

}

}

What works:

• AttachDeveloperTools() executes successfully (confirmed via Console.WriteLine after the call)

• F12 opens the built-in in-process DevTools inspector

• The MCP server discovers the app — it returns availableClients with the correct app name and PID

• AvaloniaUI.DiagnosticsSupport.Avalonia.dll is present in the build output

• No old Avalonia.Diagnostics DLL in the output (no conflict)

What fails:

• Both attach-to-app and attach-to-file MCP tool calls time out with: "TimeoutException: The operation has timed out."

• The app has zero TCP connections (netstat shows nothing for the app PID)

• No AVDT.Discovery named pipe found on the system

• No error dialogs or console errors from the app during connection attempts

What we investigated:

1. Confirmed the app runs in Debug mode (checked process command line)

2. Confirmed AttachDeveloperTools() runs without exceptions (wrapped in try/catch)

3. Confirmed ACCELERATE_LICENSE_KEY is set in both the app's environment and the MCP server config

4. Confirmed no firewall rules blocking avdt, Avalonia, or the app

5. Decompiled DeveloperToolsExtensions.AttachDeveloperTools() — discovery uses named pipes (AVDT.Discovery). The

MCP successfully discovers the app, but the subsequent connection step (which uses HTTP callback) times out

6. The app opens no listening ports, suggesting the discovery listener may not be fully initializing despite the method returning successfully

Suspicion:

The discovery pipe mechanism may not be fully working — the MCP can enumerate processes but the actual named pipe connection/HTTP callback handshake fails silently. This could be:

• The UI components key is not valid for MCP and a separate MCP-specific key is required that isn't available on the trial

• A .NET 10 compatibility issue

• Missing configuration beyond AttachDeveloperTools()

Questions:

1. Is the UI components license key (avln_on_key:v1:...) the correct key for ACCELERATE_LICENSE_KEY, or does MCP require a separate key?

2. Does the 30-day Accelerate Business trial include MCP server access?

3. Is there a known compatibility issue with .NET 10 (net10.0-windows)?

4. Is there any additional configuration needed beyond AttachDeveloperTools() for the MCP connection to work?

[seltzdesign]

"Does the 30-day Accelerate Business trial include MCP server access?"

Read the last line..

[MikeCodesDotNET]

It's included in the trial. We need to update the docs to make it clearer.

[dmealo]

Cool. And what about the issues with it not working?

[maxkatz6]

Hey, sorry for the long delay. I just released 2.2.0-beta3, which should improve stability on several layers.
Please update both DevTools and DiagnosticsSupport.

User flow is the same, but there are also two new env variables you can set:
• AVALONIA_PREVIEWER_EXPERIMENTAL - by default is true, set false to use old previwer with attach-to-file (old implementation might work better on complex solutions, feedback is welcomed)
• AVALONIA_TOOLS_LOG_LEVEL - by default is "information", set to "debug" for more detailed logs