Roblox UI

How Roblox UI works at the engine level + how to build it with Fusion 0.3.

Sources: create.roblox.com/docs/ui (engine primitives), elttob.uk/Fusion/0.3 (Fusion docs), github.com/dphfox/Fusion (source).

For deep dives see:

• references/roblox-ui-primitives.md — full GuiObject / layout / input reference
• references/design-guidelines.md — framework-agnostic UX, spacing/type/color scales, states, motion, accessibility
• references/fusion-instances.md — New / Hydrate / [Children] / [OnEvent] / [OnChange] / [Out] / [Attribute] / [Child] reference
• references/fusion-state.md — Value, Computed, Observer, peek, use, animation primitives

Integration Policy

This skill describes preferred patterns; it does not authorize rewriting existing UI. Apply rules to new components and to changes the user explicitly asks for. Match the project's chosen UI framework. If the codebase uses Roact, don't migrate to Fusion unprompted. If existing components mix offset and scale, follow that mix. If there's already a theme module, use it — don't create a parallel one. Design Guidelines are recommendations, not enforcement.