What is Qt?

Qt is a free, cross-platform toolkit that helps developers create graphical user interfaces (GUIs) and other software that can run on Windows, macOS, Linux, Android, iOS and more. It provides ready-made building blocks like buttons, windows, and graphics, so you don’t have to code everything from scratch.

Let's break it down

  • Free: You can download and use Qt without paying, especially the open-source version.
  • Cross-platform: Write your code once, and the same program works on many different operating systems.
  • Toolkit: A collection of pre-made pieces (widgets, layouts, graphics) that you can assemble to build an app.
  • Graphical user interface (GUI): The visual part of a program that users interact with - windows, buttons, menus, etc.
  • Building blocks: Ready-made components that save you time, like a ready-made “OK” button or a text box.

Why does it matter?

Qt lets developers create professional-looking apps quickly and reach users on many devices without rewriting code for each platform. This saves time, reduces bugs, and makes it easier for small teams or solo programmers to compete with larger companies.

Where is it used?

  • Desktop applications such as the KDE Plasma desktop environment and the music player Clementine.
  • Embedded systems like car infotainment screens and medical devices.
  • Mobile apps, for example the popular drawing app “SketchBook” on Android and iOS.
  • Industrial control panels and robotics software that need a reliable, consistent UI across different hardware.

Good things about it

  • Write once, run everywhere - high code reuse across platforms.
  • Rich set of widgets and graphics tools, including support for modern UI designs.
  • Strong community and extensive documentation, plus commercial support if needed.
  • Good performance; compiled C++ core runs fast, and it also offers bindings for Python, JavaScript, etc.
  • Built-in tools for internationalization, making it easy to translate apps.

Not-so-good things

  • Learning curve can be steep, especially the signal/slot mechanism and the build system (qmake or CMake).
  • The open-source version’s licensing (LGPL) may require you to expose some parts of your code, which can be a concern for proprietary projects.
  • Large binary size; even simple Qt apps can be bigger than native equivalents.
  • Occasionally lagging behind the newest OS features, requiring workarounds to use the latest platform capabilities.