# Flutter AI rules — Colour, type, documentation and accessibility

Colour schemes, fonts, dartdoc conventions and accessibility.

_Verbatim from [flutter/flutter docs/rules/rules.md](https://github.com/flutter/flutter/blob/main/docs/rules/rules.md), split across four files only to keep each under the repo's 250-line
cap. Re-fetch periodically to stay current; do not hand-edit._

#### Contrast Ratios

* **WCAG Guidelines:** Aim to meet the Web Content Accessibility Guidelines
  (WCAG) 2.1 standards.
* **Minimum Contrast:**
    * **Normal Text:** A contrast ratio of at least **4.5:1**.
    * **Large Text:** (18pt or 14pt bold) A contrast ratio of at least **3:1**.

#### Palette Selection

* **Primary, Secondary, and Accent:** Define a clear color hierarchy.
* **The 60-30-10 Rule:** A classic design rule for creating a balanced color scheme.
    * **60%** Primary/Neutral Color (Dominant)
    * **30%** Secondary Color
    * **10%** Accent Color

#### Complementary Colors

* **Use with Caution:** They can be visually jarring if overused.
* **Best Use Cases:** They are excellent for accent colors to make specific
  elements pop, but generally poor for text and background pairings as they can
  cause eye strain.

#### Example Palette

* **Primary:** #0D47A1 (Dark Blue)
* **Secondary:** #1976D2 (Medium Blue)
* **Accent:** #FFC107 (Amber)
* **Neutral/Text:** #212121 (Almost Black)
* **Background:** #FEFEFE (Almost White)

### Font Best Practices

#### Font Selection

* **Limit Font Families:** Stick to one or two font families for the entire
  application.
* **Prioritize Legibility:** Choose fonts that are easy to read on screens of
  all sizes. Sans-serif fonts are generally preferred for UI body text.
* **System Fonts:** Consider using platform-native system fonts.
* **Google Fonts:** For a wide selection of open-source fonts, use the
  `google_fonts` package.

#### Hierarchy and Scale

* **Establish a Scale:** Define a set of font sizes for different text elements
  (e.g., headlines, titles, body text, captions).
* **Use Font Weight:** Differentiate text effectively using font weights.
* **Color and Opacity:** Use color and opacity to de-emphasize less important
  text.

#### Readability

* **Line Height (Leading):** Set an appropriate line height, typically **1.4x to
  1.6x** the font size.
* **Line Length:** For body text, aim for a line length of **45-75 characters**.
* **Avoid All Caps:** Do not use all caps for long-form text.

#### Example Typographic Scale

```dart
// In your ThemeData
textTheme: const TextTheme(
  displayLarge: TextStyle(fontSize: 57.0, fontWeight: FontWeight.bold),
  titleLarge: TextStyle(fontSize: 22.0, fontWeight: FontWeight.bold),
  bodyLarge: TextStyle(fontSize: 16.0, height: 1.5),
  bodyMedium: TextStyle(fontSize: 14.0, height: 1.4),
  labelSmall: TextStyle(fontSize: 11.0, color: Colors.grey),
),
```

### Documentation

* **`dartdoc`:** Write `dartdoc`-style comments for all public APIs.


#### Documentation Philosophy

* **Comment wisely:** Use comments to explain why the code is written a certain
  way, not what the code does. The code itself should be self-explanatory.
* **Document for the user:** Write documentation with the reader in mind. If you
  had a question and found the answer, add it to the documentation where you
  first looked. This ensures the documentation answers real-world questions.
* **No useless documentation:** If the documentation only restates the obvious
  from the code's name, it's not helpful. Good documentation provides context
  and explains what isn't immediately apparent.
* **Consistency is key:** Use consistent terminology throughout your
  documentation.

#### Commenting Style

* **Use `///` for doc comments:** This allows documentation generation tools to
  pick them up.
* **Start with a single-sentence summary:** The first sentence should be a
  concise, user-centric summary ending with a period.
* **Separate the summary:** Add a blank line after the first sentence to create
  a separate paragraph. This helps tools create better summaries.
* **Avoid redundancy:** Don't repeat information that's obvious from the code's
  context, like the class name or signature.
* **Don't document both getter and setter:** For properties with both, only
  document one. The documentation tool will treat them as a single field.

#### Writing Style

* **Be brief:** Write concisely.
* **Avoid jargon and acronyms:** Don't use abbreviations unless they are widely
  understood.
* **Use Markdown sparingly:** Avoid excessive markdown and never use HTML for
  formatting.
* **Use backticks for code:** Enclose code blocks in backtick fences, and
  specify the language.

#### What to Document

* **Public APIs are a priority:** Always document public APIs.
* **Consider private APIs:** It's a good idea to document private APIs as well.
* **Library-level comments are helpful:** Consider adding a doc comment at the
  library level to provide a general overview.
* **Include code samples:** Where appropriate, add code samples to illustrate usage.
* **Explain parameters, return values, and exceptions:** Use prose to describe
  what a function expects, what it returns, and what errors it might throw.
* **Place doc comments before annotations:** Documentation should come before
  any metadata annotations.

### Accessibility (A11Y)
Implement accessibility features to empower all users, assuming a wide variety
of users with different physical abilities, mental abilities, age groups,
education levels, and learning styles.

* **Color Contrast:** Ensure text has a contrast ratio of at least **4.5:1**
  against its background.
* **Dynamic Text Scaling:** Test your UI to ensure it remains usable when users
  increase the system font size.
* **Semantic Labels:** Use the `Semantics` widget to provide clear, descriptive
  labels for UI elements.
* **Screen Reader Testing:** Regularly test your app with TalkBack (Android) and
  VoiceOver (iOS).