Disable round corners (or “rounded corners”) on Windows 11

A simple utility to disable round corners of Windows 11 without hacks.

How to use it?

1. Open Visual Studio Developer Prompt.
2. Run the command in DisableRoundCorners.cc to compile it.
3. Launch DisableRoundCorners.exe.

You can compile it once, then put a shortcut to it in your start-up folder (run shell:startup to open this folder).

How does it work?

1. It registers a Windows event hook that monitors any new top-level windows (i.e., “windows” in the usual sense) and calls DwmSetWindowAttribute to disable the round corners of each new window.
2. After registering the hook, it also iterates through all existing top-level windows and disable the round corners of them.

Goods/Bads/Should-Knows.

• Does not modify system DLL.
• Does not require administrative privilege to install/run.
• If run unelevated, it doesn’t affect windows in elevated processes. This is by design and can only be fixed (without elevation) using UI access, which requires signing the code with a trusted certificate and placing it in a secure location. (A very costly thing for me, so no.)
• If you log off (or shut down or restart the computer) but decide to cancel the log-off due to another program blocking shutdown, then this program might have exited. Consequently, after a cancelled log-off, any new windows might have round corners by default. This is by design and a good thing, because this program doesn’t try blocking shutdown.