Design To Code

Design-to-Code Skill

1. Asset Management

1.1 Organization

All assets must be placed in the packages/app_ui/assets/ directory following this structure:

• SVGs: assets/svg/
• Icons: assets/svg/icons/
• SVG Images: assets/svg/images/
• Raster Images: assets/images/ (PNG, JPEG, WebP — e.g., photos, hero banners)
• No Feature Folders: Do not create feature-specific subfolders (e.g., login/, auth/) within these asset directories. Keep the structure flat by asset type to avoid issues if an asset is later reused in another feature.

1.2 Verification & Generation

1. Verify: Before adding an asset, check packages/app_ui/assets/ to see if it already exists.
2. Add: Place the new asset in the appropriate folder.
3. Generate: Run melos run generate to update the AppAssets class.
4. Usage: Use AppAssets to reference the asset in code:

``dart AppAssets.icons.google.svg(); ``

1.3 Handling Missing or Unplaced Assets

When extracting from Figma via the MCP server, assets might not be marked for export or could be missing entirely:

1. Detection: If the MCP server cannot locate or export an expected visual asset.
2. Placeholders: Use a standardized placeholder widget to maintain layout integrity. Always include a TODO comment for traceability:

``dart const SizedBox(width: 120, height: 120); // TODO(design): Replace with exported asset. @Source: > > ``

1. Notification: Explicitly notify the user that the asset was missing from the exportable Figma assets and request they mark it for export or provide it manually. NEVER use the Figma MCP API asset URL (https://www.figma.com/api/mcp/asset/...) directly in the code (e.g. via Image.network).

1.4 Asset Usage

1. No Local Package Constants: NEVER define const _kUiPackage = 'app_ui'; locally.
2. Use Exported kUiPackage: Rely on the exported kUiPackage from app_ui when required, but avoid using it outside the package if possible.

2. Typography & Colors

2.1 Colors

1. Use curated, HSL-tailored colors defined in app_colors.dart.
2. Avoid hardcoded hex values (Color(0xFF...)) in UI; always use context.$.colors.
3. No Private Color Classes: Never create private static classes, state variables (e.g., static const _color = Color(...)), or files for colors inside views or widgets. All colors MUST be defined in app_colors.dart.

Handling Unstructured Palettes

If the design lacks a defined palette or uses inconsistent, ad-hoc hex codes (e.g., from junior designers):

1. Consolidate: Identify the core, most frequently used colors representing the brand or theme.
2. Map: Map these extracted core colors to the existing semantic tokens in app_colors.dart (e.g., primary, secondary, surface).
3. Consult: Strictly prohibit hardcoding random hex values. If a new semantic token is genuinely needed to represent a consistent design pattern, consult the user rather than creating ad-hoc colors.

2.2 Typography

1. Reuse: Maximize reuse of existing styles in AppTextTheme.
2. Customization: If a specific style isn't available, use the any field combined with copyWith to maintain consistency while allowing flexibility.

``dart Text('Design Text', style: context.$.style.any.copyWith(fontSize: 18, color: context.$.colors.primary)) ``

2.3 Spacing

1. Map Figma spacing values directly to AppSpacing tokens.
2. Nearest Match Rule: If an exact token does not exist for a Figma value, round to the nearest available token. If equidistant, prefer the smaller token (e.g., if Figma shows 18px, use AppSpacing.md (16px) over AppSpacing.lg (20px) since 18 is equidistant).
3. Always prefer AppSpacing constants over hardcoded double values.

2.4 Internationalization (i18n)

1. No Hardcoded Strings: Never hardcode user-facing strings in the UI.
2. Translation Files: Add strings to the appropriate domain section in the i18n files (using slang).
3. Usage: Access translations using context.$.tr (e.g., context.$.tr.auth.login.title).
4. Direct Localization: Use localization directly within the respective _view.dart files (or their specific local widgets). NEVER pass translated strings down from parent pages or via ViewProps.
5. Generation: Run melos run translate after updating translation files.

3. Atomic Design & Widgets

Break the design into reusable components. Before creating anything:

1. Logical Structuring: Do not blindly mirror the exact layer structure of the Figma file. Designers sometimes take shortcuts or use non-logical groupings. Analyze the layout logically and implement a clean, efficient Flutter structure.
2. Extract BEFORE Implementing View: If Figma has a distinct frame/group (e.g., complex forms, headers, custom inputs, distinct visual blocks), you MUST extract it to packages/app_ui/lib/src/widgets/ before writing the feature's _view.dart file. The _view.dart file must ONLY compose pre-built app_ui widgets. DO NOT build UI blocks directly inside _view.dart and absolutely DO NOT create private widget classes (e.g., _FeatureHeader, _CustomAction) inside the _view.dart file.
3. Generic Naming: Always use generic, domain-agnostic names for extracted widgets. For example, name a button YzPrimaryButton rather than YzLoginButton, or YzIconButton rather than _UserAvatarButton, even if it is currently only used on a specific screen.
4. Widget Properties: Default dimensions (height, width, etc.) should be defined as constructor properties with their default values set directly in the constructor. Do not define them as private constants outside the class (e.g., avoid const _headerHeight = 295.0;).
5. Check Widgets: Verify packages/app_ui/lib/src/widgets/ for existing components and their design @Source.

• Use grep_search to find matching @Source breadcrumbs (e.g., Login > Hero > CTA).
• Do not extract a component that is already synced.

1. Deduplication: A reusable widget (e.g., a primary button) may appear on many pages. Match by visual similarity — not by page location.

To efficiently find matches in a large codebase:

• Search: Use grep_search on the widgets directory for specific @Style or @Layout tokens (e.g., @Style:.*Bg: primary).
• Inspect: Use view_file to read the specific candidate .dart files to verify properties.

If the element visually matches, reuse that class. Do not create a duplicate.

1. Imports: Always consume via package:app_ui/app_ui.dart. Avoid internal file imports.

> [!NOTE] > For widget implementation rules (naming, structure, exports, and code annotations), follow the [UI Widget Creation Skill](create-ui-widget.md).

4. Feature Implementation

4.1 Feature Setup

Follow the [Feature Creation Skill](create-feature.md) to set up the directory structure.

• Complex features (like Auth) should have sub-folders for each page (e.g., auth/login/).
• Permissions: If the target feature folder does not exist, you must ask for user permission before creating the directory structure.

4.2 Building Views

Implement the view for the target platform (e.g., mobile):

• login_view.dart (Mobile)
• If required later, implement login_view_web.dart (Web).
• Refer to [Feature Creation Skill](create-feature.md) for state binding and performance optimization (MemoizedView).
• Use AppSpacing and AppAssets consistently.

5. Figma Tracking (Manifest & Code)

To maintain a single source of truth and prevent redundant extraction, we use a Code-as-Truth approach for widgets, and a dedicated manifest for file tracking.

5.1 Project-Level Tracking

packages/app_ui/figma_manifest.yaml acts as the manifest to track active Figma file(s) and sync status:

figma_file_ids:
  - id: ""
    name: "Main App Design"
last_sync: ""

5.2 Component Tracking (Code-as-Truth)

We do not use a centralized markdown table. Instead, components are tracked directly via doc-comment annotations (see [UI Widget Creation Skill](create-ui-widget.md#4)).

• Tracking: Ensure every new component has the strict 4-line @UI, @Source, @Style, and @Layout annotations directly above the class.

> [!NOTE] > Design Evolution: If a Figma design has changed since the last sync, update the @Status of the affected widget's doc-comment to outdated.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: anoopsg
• Source: anoopsg/agent_rules
• License: MIT

Install and usage instructions live in the source repository linked above.