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Tessel

Tessel

A small, declarative language for desktop apps. Write your UI the way you think about it, and get a fast native app for macOS and Windows.
Get startedYour first appLearn to program

A whole app in a few lines

Section titled “A whole app in a few lines”
app Counter(width: 320, height: 200) {
    state count = 0


    VStack(spacing: 12) {
        Text("Count: {count}")
            .font(size: 32, weight: .bold)


        HStack(spacing: 8) {
            Button("-") { count -= 1 }
            Button("+") { count += 1 }
        }
    }
    .padding(24)
}
The Counter app, showing Count: 3 with minus and plus buttons

Run it with tessel run counter.tsl. No project files, no imports, no build configuration: a folder of .tsl files is a program.

Why Tessel

Section titled “Why Tessel”

Declarative

Describe what the screen shows for the current state. When state changes, Tessel updates the window for you.

Native and fast

Programs compile through LLVM to small native executables. The UI is drawn on the GPU by Tessel’s own renderer.

Few rules to learn

One kind of block, value types only, no imports, and errors as optionals. Every error message says what to do next.

macOS and Windows

The same code builds a .app bundle on macOS and an .exe on Windows.

Built for real apps

Section titled “Built for real apps”
A todo list app with three items, one done, and an All / Active / Done picker

Structs, enums, lists and dictionaries; text fields, toggles, pickers, tabs and a code editor; about 60 built-in icons; files, processes and the network, with callbacks that update your UI safely. See the todo list tutorial.

An IDE written in Tessel

Section titled “An IDE written in Tessel”
The Tessel IDE with a file explorer, a tabbed code editor and a problems panel

Type tessel in a project folder to open the Tessel IDE: a file explorer, tabbed editor with syntax colors and live errors, and one-click run, build and packaging. It’s a Tessel app itself. Read more.