How to identify which program has left a portion of its UI floating on my screen?

You are most likely experiencing a Chrome bug that results in undismissable tooltips.

Basically, if you hover over something on a webpage and then your mouse moves outside the window in an unexpected way (such as minimizing the window), the tooltip will appear after the window disappeared, and there is no way to dismiss the tooltip (since the source window no longer gets mouse move messages, and as far as it's concerned, you're still hovering).

To get rid of the tooltip, you can

1. Find the tab it came from and just move your mouse around. The tooltip should disappear. (Unfortuantely, there's no easy way to determine which tab the tooltip came from, so you'll have to guess. It has no direct association in the window hierarchy; its parent is the desktop window.)
2. If you can get the tooltip's HWND, you can send it WM_CLOSE and it will go away. (see below)
3. Exit Chrome (or other offending app)

Note that this bug affects software based on Chrome as well, such as Blink-based browsers (Edge and Opera) and things built on Electron (Slack and hundreds of others).

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To answer the question itself, you can find the process that owns the tooltip by using a debugging tool like Spy++ or WinCheat.

Drag the window picker tool over the tooltip and it will show you the window's details, including the owning process.

If you then go to the Actions tab, you can send the tooltip window a WM_CLOSE message and it will go away. (Be careful with this tool -- great power, great responsibility. Apps may not expect windows to be closed out from under them. Doing this doesn't appear to make Chrome crash.)

I noticed that what looks like a tooltip saying "Increase Indent" is floating homeless on my screen.

There are 2 possibilities:

1. A glitch that hasn't been redrawn correctly by the underlying window manager code

2. A real Window that cannot be moved/closed

A glitch that hasn't been redrawn correctly

• to remove it toggle the Show Desktop button on the far right of the taskbar.

How can I remove an unwanted fragment of old GUI on my screen? (Windows 7) - Super User shows some other possible solutions:

• change the theme of your windows from Aero to Classic and then back to Aero again.
• Start Menu > Shut Down > Switch User, On Welcome screen just log back in

As per comments you can also try:

• Restarting Windows Explorer will do the trick too, most of the time. If not, restart dwm.exe

A real Window that cannot be moved/closed

You can use Process Explorer's "Find Window's Process" feature (the crosshairs on the toolbar of the Process Explorer window). Click and drag it over the window you want to identify, and Process Explorer will highlight the process it belongs to.

Source I can't remove a tiny window, answer by cyanic

When you know which process the windows belongs to you can choose to terminate that process by using the Task Manager.

Use Spy ++ (SPYXX.EXE) to find this buggy program. https://docs.microsoft.com/en-us/visualstudio/debugger/introducing-spy-increment

This article should help you: https://docs.microsoft.com/en-us/visualstudio/debugger/how-to-use-the-finder-tool