Introduction

Masque is a UI language and embeddable runtime for Rust applications. You describe your interface in Masque documents (.masque files). Masque compiles them to bytecode, runs them on a small stack VM inside your process, and reconciles the result into a live widget tree that a renderer draws. A Skia backend ships with the crate.

Who it is for

Masque is for Rust programs that already own a window and a frame loop and want a better way to build their interface: games, creative tools, editors, and embedded displays. It is a library you call each frame, not a framework your app moves into.

How it fits together

Your application owns all the state and logic. A Masque document is a projection of that state:

• Host state flows in. You hand the runtime values by name, and the document reads them as plain identifiers.
• Events flow out. The document calls event("name", ...), and your registered handler decides what happens.
• The document never mutates your app. It cannot reach in, so every change to your data happens in your Rust code.

Inside the runtime, a document passes through four stages, each depending only on the one before it:

Stage	Produces
Scanner and parser	An AST
Compiler	Bytecode, compiled once per load
VM	Widget descriptors, re-run when state changes
Builder and reconciler	Updates to the live widget tree, applied in place

The widget tree does layout (flexbox and grid), springs, hit-testing, and events. Only painting goes through the Surface trait, which is why the renderer can be swapped.

Where to go next

• Installation: add the crate and its native dependencies.
• Quick start: from an empty project to a hot-reloading window.
• Design principles: the rules a document can rely on.