November 10, 2020 by Olivier Goffart and Simon Hausmann

Introducing SixtyFPS

We’re Olivier & Simon - two enthusiastic software engineers who enjoy developing software for product teams. Today we’d like to introduce you to our new venture.

What is SixtyFPS?

A fresh, new graphical toolkit for desktop apps and embedded devices

We're building a product to make UI development faster and easier, no matter what programming language, platform, or form-factor. Our toolkit consists of the following key components:

  • A design-friendly markup language for UI elements
  • A run-time library with APIs in C++, Rust and JavaScript
  • An optimizing compiler to compile designs to native C++/Rust

Express user interface constraints and relations

Designing a user interface starts with primitive graphical elements, such as shapes or images. The design you envision requires placing these elements on a display surface, based on a coordinate system, to produce a visual hierarchy. We use our .60 markup language to define these elements, where and how they are placed, and how they exchange data. Let’s have a look at an example:


Hello World Example


Hello World Screenshot

This snippet of code describes a rectangle and a text element that render a button. It looks like a blend of JSON and CSS, which is intentional. We took the structural aspect of JSON, added the nice aspects of CSS, such as numbers with absolute or relative lengths, named colors, and layouts. We also added an automatic property binding system.

There’s a lot more to unpack here. Our constantly-evolving markup language reference documentation is a good starting point for a deeper dive. You can also play with the example above in our experimental online editor.


Screenshot of Printer Demo
Screenshot of the printer demo

As chipsets become faster and RAM becomes cheaper, the scale at which computing devices are produced for our appliances grows. In our experience, software that uses less CPU and memory will always have an edge. An optimized software stack means that save money on the per-unit hardware cost.

We are committed to providing that edge through:

  • Our .60 markup compiler generates a carefully designed memory layout. All the components and properties are in one flat memory allocation that is compact and requires minimal malloc calls.
  • Our lightweight property system evaluates binding expressions lazily.
  • Our rendered uses GPU acceleration by default.

Check out our demos online to get a feeling for how smooth UIs can be, even when compiled to run in a web browser simulation.

Integrate into different languages

One particular aspect of software development that we enjoy is the diverse landscape. Different teams use different programming languages, with their unique constraints and talent pools. We embrace this diversity and believe that a good UI toolkit should support this by making every language feel as if it’s the native toolkit. It’s crucial to provide idiomatic APIs, so that teams can feel right at home. We do this by making sure that:

  1. Our C++ integration uses modern C++ 17 and comes with built-in CMake support.
  2. For Rust developers, we offer a convenient crate, integration, and even a proc-macro.
  3. Our NodeJS integration is available via npm and allows you to write signal handlers in JavaScript and even provide custom data models.

Check out our API documentation for the different languages.

We choose to first support this set of languages because it is the implementation language, another low level language, and a dynamic language. We believe that it will be easy to extend the integration into more programming languages later.

What’s next?

Our project is still in an alpha state. We would love to get your feedback; give it a try. You can provide feedback or join our discussions on our GitHub site.

SixtyFPS in its current shape is a highly customizable, compelling starting point for new UI product developments and prototypes.

We're be happy to engage in contracting work to explore custom UI development projects with SixtyFPS.

Get in touch with us via email.


Slint is a declarative GUI toolkit to build native user interfaces for desktop and embedded applications written in Rust, C++, JavaScript, and Python. Find more information at or check out the source code at