Why Rectangle’s Maximize Isn’t the Same as True Fullscreen

A real, specific report on Rectangle mac‘s issue tracker (issue #1350) describes a user’s confusion after using Rectangle mac‘s Maximize action: unlike macOS’s native fullscreen (triggered by holding Option and clicking the green button), Rectangle app‘s Maximize still leaves a visible sliver of whatever was behind the window, rather than fully hiding everything else the way native fullscreen does. This isn’t a bug — it’s a direct consequence of what maximize window to fill screen‘s Maximize is actually designed to do, and understanding the distinction clears up a genuinely common point of confusion.

What the two features actually are, at a technical level

Native macOS fullscreen (Option-click the green button, or the standard click-and-hold menu) moves an app into its own Space — a separate virtual desktop dedicated to that one app, with the menu bar and Dock hidden entirely. It’s not resizing the window; it’s changing what kind of object the window even is, from macOS’s perspective.

keyboard window management‘s Maximize does something categorically different: it resizes and repositions an ordinary window to fill the available screen space, while keeping it as an ordinary, normal window the whole time — same Space, same menu bar, same Dock, just resized to be as large as possible within that space. This is a deliberate design choice, not an oversight: a window has to remain an ordinary resizable window for any of Rectangle’s other actions (Restore, Left Half, moving it to another display) to keep working on it afterward. If Maximize actually triggered native fullscreen, the window would become a Space, and none of Rectangle’s other shortcuts could act on it anymore — the entire premise of a fast, all-keyboard workflow across multiple positions depends on windows staying as ordinary windows.

Why you sometimes see a sliver of another window

Because Maximize resizes within the available screen space rather than replacing the whole screen with a dedicated Space, the “available screen space” calculation itself matters. If a menu bar auto-hide setting, a specific display’s usable area calculation, or (per the reasoning covered elsewhere in this series) a gap setting is in play, the resulting maximized window can end up very slightly smaller than the full physical screen, exposing a thin edge of whatever’s behind it. This is consistent with — though a different symptom from — the top-edge gap issues covered in the dedicated troubleshooting article on that topic; both trace back to Rectangle calculating an available area that’s marginally different from the true edge-to-edge screen dimensions in certain configurations.

Which one should you actually use?

Neither is objectively better — they serve different goals:

Use native fullscreen when you want one app to have your complete, undivided attention, with the Dock and menu bar out of the way entirely, and you don’t need to quickly switch that window to a half or third afterward. Presentations, video playback, and distraction-free writing are common fits.

Use Rectangle’s Maximize when you want a window as large as possible while still being able to instantly resnap it to a half, quarter, or third with another shortcut, glance at the menu bar for the time or a status icon, or use Restore to snap it back to whatever it was doing before. If your workflow involves switching between full-width and split-screen throughout the day, Maximize is the compatible choice, since native fullscreen exits you out of the Space entirely to do anything else.

If you specifically want something closer to native fullscreen, without leaving Rectangle’s action set

Almost Maximize (bindable in Rectangle’s fuller action list, covered in the shortcuts cheat sheet) resizes to roughly 90% of the screen by default — smaller than a true edge-to-edge maximize, but deliberately leaving a visible margin so you’re never confused about whether you’re looking at a maximized ordinary window or a full-Space fullscreen app. If your actual goal is “as large as possible, unambiguously still a normal window,” Almost Maximize is arguably a better fit than plain Maximize specifically because it doesn’t try to visually resemble fullscreen at all.

The core distinction to remember

Rectangle never puts a window into native fullscreen mode as part of any of its actions — that’s a deliberate boundary, not a missing feature. Every Rectangle action, including Maximize, keeps a window as an ordinary, still-manageable window. If you want the actual Space-based fullscreen experience, that has to come from macOS’s own fullscreen control, used separately from Rectangle rather than through it.