Go to this link, click “Assets” to expand the list if it is not already expanded, and select “UndertaleModTool_vX.X.X.X-Windows.zip”.

You can also select the “SingleFile” one, which may make the extraction faster when using Windows Explorer. (bundles all the files into one executable).

Extract the file by right-clicking and selecting “Extract All…” from the menu.

Ensure “Show extracted files when complete” is checked and click Next.

This extraction can be performed with other archive utilities, such as 7-zip.

After extraction completes, find “UndertaleModTool.exe” in the folder and double-click it. A new window should appear.

UndertaleModTool does not have a GUI (Graphical User Interface) version available for MacOS or Linux. This is because the GUI is built with WPF.

In short, WPF is only compatible with Windows. While you could run the Windows version of UTMT with Wine, it is highly unstable (crashes from simple actions) and not guaranteed to work.

There is a CLI (Command Line Interface) available for ALL platforms, however it is very, VERY primitive. You can download that from the releases page mentioned above.

Instead, there has been a port to Avalonia in the works since May 18th, 2025. Avalonia is another GUI framework with the main difference being that it is cross-platform.

You can download that from this pull request. Keep in mind it is a work-in-progress.

Download it by selecting either platform (MacOS/Linux) and extract the files. (the extraction procedure is close to the Windows procedure on at least some Linux distributions).

Refer to the pull request for progress on the port.