NiceGUI is an open-source library designed for Python that empowers developers to craft web-based graphical user interfaces (GUIs) using solely Python code. It boasts an approachable learning curve and simultaneously allows for sophisticated customizations. Adopting a backend-first approach, NiceGUI takes care of all web development intricacies, enabling developers to concentrate on their Python code. This framework is well-suited for diverse applications, from simple scripts and dashboards to robotics, IoT systems, smart home automation, and machine learning initiatives. It is constructed on FastAPI for backend functions, utilizes Vue.js for frontend interactions, and incorporates Tailwind CSS for styling aesthetics. With NiceGUI, developers can effortlessly create various elements, including buttons, dialogs, Markdown content, 3D visualizations, plots, and much more—all within a Python-centric environment. Furthermore, it facilitates real-time interactivity via WebSocket connections, allowing for immediate updates in the browser without needing to refresh the page. Additionally, NiceGUI provides a plethora of components and layout configurations, like rows and columns, ensuring versatile design possibilities for users.