Windows users will be familiar with a feature that allows previewing window contents by hovering over their taskbar icons. If you want this in macOS as well, the only way you’re going to get it is via a third-party app.

Dock previews are DockDoor’s main functionality, with the added bonus of an alternative alt-tab feature that includes window previews. It’s an open-source app, very easy to set up and use, though still not quite perfect.

Preview app windows via the Dock
If an app window is active and present in the Dock, you can preview its contents by hovering over its Dock icon. The preview can be resized to suit your preferences, and you can add a delay or customize the window buffer.

Unfortunately, the feature won’t work for minimized apps, and if the window is partially offscreen, that part of the window will be cut off in the preview as well.

The previews are also not updated as frequently as you might expect. If the window contents change, it may take around half a minute for the preview to be updated as well.

Alt-tab with previews
DockDoor’s other main feature is its alt-tab functionality. Using the Ctrl+Tab hotkey, you can cycle between active windows and switch between them as you would with Alt+Tab. The main benefit is that you’ll also be able to preview window contents while doing so, just like on Windows.

This feature works well, though again, only for windows that aren’t minimized. Also, if you have a lot of open windows, cycling between them gets more difficult, as only three can be displayed on the screen at a time.

Promising, but still a work in progress
DockDoor is a great app in principle, but it still needs work. The Dock preview feature has some restrictions that limit its use cases, while the Alt-tab alternative needs a bit more polish, and a customizable hotkey to avoid conflicts with browsers and other apps.

What's New:

Version 1.37.0: 

New Features

• Shift+click on an icon in the dock opens a new app window - default OFF
• Auto-open windows for windowless apps when selected in switcher.

Improvements & Stability

• Apps with no windows now respect relevant appearance options.
• Fix window previews rendering too wide.
• Fix music widget rendering in random sizes.
• Window titles no longer scroll, now they truncate in the center by default.
  • Customizable title overflow styles for window titles - can configure types of truncation or switch back to marquee for window titles

Bug Fixes

• Improved Cmd+Tab reliability
  • Works when window switcher is off
  • App matching works correctly
  • Previews dismiss properly
• Tapping music widget background now switches apps correctly
• Media widget no longer resizes on hover
• Title styles no longer inflate preview width
• Fix artwork being stale when new media has no artwork
• Window switcher respects limit to active app only for windowless apps
• Cmd-tab preview should no longer remain on screen consistently (better coverage)

Screenshots:

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