Linux GUI toolkits might sound confusing, but they define the look and feel of modern Linux desktops. Here's everything you need to know about them.

Linux GUI Programs Use Toolkits to Make Development Easier

The X Window System is the main display server in use on Linux desktops today. While it may provide elements of a graphical interface, it doesn’t supply any user interface elements by itself. This is a deliberate design choice on the part of the original developers.

X doesn’t know how to draw window decorations. It doesn’t draw the buttons in windows or lay out any text elements. All of these things are handled by the toolkit.

X toolkits offer developers a way to define graphical elements without having to do it all manually. Instead of writing out code to allow users to pick files from a dialog box, they can farm this out to a library instead.

These toolkits also provide a look and feel among applications that use them. Windows and macOS employ a similar strategy, but they only have one main style that they enforce.

Since Linux doesn’t have a standard GUI, different programs often use different toolkits. To complicate things further, you can use the same Linux toolkits to build programs for these other major platforms.

It's possible to install X apps like xcalc that use the original toolkit. If you do, you'll notice that they look very old-school.

The Two Major GUI Toolkits: Qt and GTK

xcalc, kcalc, and GNOME calculators on an XFCE desktop

The two major toolkits used on modern Linux desktop environments today are Qt and GTK. The former is associated mainly with KDE Plasma, as the original KDE was built using Qt and the project has stuck with it to this day.

GNOME and Xfce use the GTK toolkit that was originally developed for GIMP because Qt had a proprietary license when it was first developed in the '90s.

Despite their association with Linux, Qt and GTK are cross-platform and you can use them on other Unix-like systems and to build Windows and macOS apps as well.

Why Two Programs on the Same Machine Can Look Very Different

Due to X’s UI agnosticism, different programs on the same machine can have widely-differing appearances. This might be one reason that Linux desktops have struggled to gain acceptance among mainstream users.

GNOME and KDE attempt to get around this by bundling applications using their favored toolkits with their systems and encouraging users to favor apps built using the main toolkit when choosing new apps to install.

Users can install any program they like on a Linux system. This approach to user interfaces is an illustration of Linux’s flexibility.

Now You Know About Linux GUI Toolkits

Toolkits define the look and feel of modern Linux apps. They streamline development by providing graphical elements to developers instead of them having to write them from scratch.

Qt and GTK underpin the modern KDE, GNOME, and Xfce desktops. They can also make Linux apps built with different toolkits that have different appearances.

Choosing a Linux desktop means choosing a toolkit underneath it. Everyone seems to have their personal favorite but which one you like the best, depends on what you expect from your desktop.