Design kit

A native look comes from Apple's parts. A custom look comes from your own parts: your sidebar row, your button, your checkbox, your icons. SwiftUI draws all of them. A kit is those parts, the numbers behind them, and one page that shows every part in every state.

Most apps keep Apple's parts and only pick an accent color (design-system skill). Build a kit when the parts themselves must change. To copy the look of an existing app, call the Skill tool with design-from-app first: it measures the app and then comes back here.

Everything lives in Sources/<App>/DesignKit/. Code for every step: parts.md.

1. Write the spec

Write design/KIT.md from kit-spec.md: three words for the feel, the tokens, the type scale, the icon rules, and one section per part with its sizes and states. Agents build from this page and review against it.

Check: every part the app's screens need has a section with its sizes and its states.

2. Tokens in three layers

DesignKit/Tokens.swift:

1. Palette: raw colors, named by hue and step (gray50, blue600). Only this file reads it.
2. Meaning: Ink.text, Ink.accent, Ink.selection, Ink.divider, with a light and a dark value each. Parts read only this layer.
3. Scales: KitType (type roles), Metric (sizes), Motion (named intents like hover and check).

A rebrand changes the palette. A dark mode fix changes the meaning layer. Neither touches a part.

Check: grep -rn 'Palette\.' Sources/ | grep -v Tokens.swift finds nothing.

3. Type

Name styles by role (title, body, label, section, meta), never by size. Use the system font unless the brand needs its own; a bundled font goes in Resources/Fonts/ with ATSApplicationFontsPath in Info.plist.in. Half-point sizes are fine when a reference needs them.

Check: views set fonts only through .kitType(...).

4. Icons

Icons decide the feel more than color does. Views name a KitIcon, never an SF Symbol or a file, so the whole set can change in one place.

• Start from SF Symbols at a fixed size and weight. Light weights read less like Apple.
• For a set of your own, draw each icon as a SwiftUI Shape from its SVG path, or make custom symbols in the SF Symbols app.
• One size, one stroke weight, one corner style for the whole set.
• A selected row may switch to the filled form.

Check: grep -rn 'systemName:' Sources/ | grep -v DesignKit/ finds nothing.

5. Parts

One file per family in DesignKit/Components/: sidebar, rows, buttons, fields, menus. Each part:

• Is a real control. Style a Button with a ButtonStyle, a Toggle with a ToggleStyle, a field with a TextFieldStyle. Never a shape with a tap gesture: it loses the keyboard, focus, and VoiceOver.
• Has every state: rest, hover, pressed, selected, focused, disabled, in light and dark. Hover uses onHover, pressed uses configuration.isPressed, disabled reads isEnabled.
• Takes a forced state for the gallery, so hover and pressed show up in a snapshot.
• Reads only meaning tokens, KitType, Metric, Motion, and KitIcon.

Check: the part matches its section in design/KIT.md in every state.

6. Window chrome

For a fully custom look, hide the title bar and draw your own top bar, and build the sidebar from kit rows instead of List. Keep the traffic lights, menus, context menus, sheets, and alerts native: users depend on them. SwiftUI cannot move the traffic lights; a small NSViewRepresentable reaches the NSWindow (parts.md, Window chrome).

A custom sidebar matches the macOS 27 system one where people would notice: the selected row's text turns semibold, the selection fill dims when the window is inactive (@Environment(\.appearsActive)), and row corners stay concentric with the sidebar (mac-design patterns.md, "Custom chrome that follows the window"). Custom glass bounces on click only on controls.

Check: the window opens at its default size, the traffic lights sit where the spec says, the custom sidebar moves with the arrow keys, and its selection dims when another window is in front.

7. Gallery

DesignKit/KitGallery.swift shows every part in every state, in light and dark, the way a storybook does. The app shows it instead of its pages when APP_KIT_GALLERY=1 is set, so the normal snapshot command captures it. Review a new part here before it goes into a screen.

Check: the gallery snapshot shows every part from design/KIT.md, and the user has seen it.

8. Checks

tools/grid-lint.sh
grep -rnE 'Color\(hex|Color\(red|\.font\(\.system|systemName:' Sources/ | grep -v DesignKit/

Both come back clean. Then build, snapshot, and run the layout-grid checks on the screens (build-and-verify skill).

Done when design/KIT.md covers every part, every part is a real control with every state, the gallery shows them all in light and dark, and the checks above come back clean.