Rhombus.WinFormsMcp

Give AI agents eyes and hands for Windows Forms apps

An MCP server that lets Claude (and any MCP-compatible agent) launch, automate, screenshot, and preview WinForms applications — without touching a mouse.

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The problem

You're building a WinForms app with an AI coding agent. The agent can read and write your code, but it's blind — it can't see what the form looks like, can't click a button to test a workflow, and can't tell if the UI it just generated actually renders correctly.

The fix

One line in your MCP config. Now the agent can:

See forms without building	render_form gives the agent a designer — the exact same rendering pipeline Visual Studio uses. Edit, re-render, iterate with no build and no human in the loop
Drive running apps	Launch processes, find elements by name/type/ID, click, type, drag-drop, take screenshots
Work in the background	Headless mode runs apps on a hidden desktop — zero focus stealing, zero disruption
Target any framework	.NET Framework 4.x, .NET Core 3.x, .NET 5–9+. Auto-detected from your .csproj

Quick start

Claude Code plugin (easiest):

/plugin marketplace add fnrhombus/claude-plugins
/plugin install winforms-mcp@claude-plugins

MCP config with npx (requires Node.js):

{
  "mcpServers": {
    "winforms-mcp": {
      "command": "npx",
      "args": ["-y", "@fnrhombus/winforms-mcp"]
    }
  }
}

Standalone (no Node required) — download the zip from Releases, extract it, and point to the exe:

{
  "mcpServers": {
    "winforms-mcp": {
      "command": "C:/path/to/winformsmcp/winformsmcp.exe"
    }
  }
}

Note: Keep the extracted folder structure intact — render_form needs the rendererhost/ subdirectory alongside the exe.

That's it. The agent can now see and interact with any WinForms application on your machine.

Tools

Category	Tools	Description
Process	launch_app attach_to_process close_app get_process_status	Start, attach to, and manage Windows processes
Discovery	find_element element_exists wait_for_element get_element_tree	Locate UI elements by AutomationId, name, class, or control type
Interaction	click_element type_text set_value select_item click_menu_item drag_drop send_keys	Click buttons, fill text boxes, select combo items, navigate menus
Visual	take_screenshot render_form	Capture running apps or render .Designer.cs to PNG

Cross-framework rendering

render_form detects your project's target framework and dispatches to a matching out-of-process host — the same rendering pipeline Visual Studio uses, so custom controls and third-party components resolve correctly.

Your project targets	Renderer host
.NET Framework 4.0–4.8.x	net48
.NET Core 3.x	netcoreapp3.1
.NET 5, 6, 7, 8, 9+	net8.0-windows

Framework-specific APIs resolve correctly too. Override with the TFM environment variable if needed.

Headless mode

Set HEADLESS=true to launch apps on a hidden Windows desktop (CreateDesktop API):

• Zero focus stealing — apps can't steal focus, show TopMost windows, or flash in the taskbar
• Full automation — element discovery, clicking, typing, and screenshots all work through UIA patterns and PrintWindow
• Mixed mode — headless and visible apps in the same session, each automatically routed to its correct desktop

{
  "mcpServers": {
    "winforms-mcp": {
      "command": "npx",
      "args": ["-y", "@fnrhombus/winforms-mcp"],
      "env": { "HEADLESS": "true" }
    }
  }
}

Note: send_keys and drag_drop require input simulation and only work on the visible desktop. Use type_text/set_value and click_element for headless processes.

Environment variables

Variable	Default	Description
HEADLESS	false	Run launched apps on a hidden desktop
TFM	auto	Lock rendering to a specific framework (net48, netcoreapp3.1, net8.0-windows)
TELEMETRY_OPTOUT	false	Disable all Application Insights telemetry (matches .NET CLI conventions)

Documentation

• Examples — common workflows and patterns
• Headless Mode — hidden desktop architecture and tool compatibility

Contributing

Contributions welcome — see issues for open items. Git hooks for commit validation and code formatting are configured automatically on first build.

Support

If you find this project useful, consider supporting its development:

• GitHub Sponsors — Monthly sponsorship with public recognition
• Buy Me a Coffee — One-time or recurring donations

Your support helps maintain and improve this project!

License

MIT