# Token conventions

These conventions MUST be followed by any agent creating or modifying tokens.

## W3C DTCG format

All tokens use the DTCG JSON format. Every token has `$value`, `$type`, and `$description`.

```json
{
  "color": {
    "brand": {
      "primary": {
        "$value": "#1B4965",
        "$type": "color",
        "$description": "Primary brand colour — deep navy. Used for primary actions, key headings, and trust-building UI elements."
      }
    }
  }
}
```

## Naming rules

### General
- Use dot notation for hierarchy in documentation: `color.brand.primary`
- In JSON, dots become nested objects
- Names are lowercase, no spaces, no special characters except hyphens for compound words
- Names must be descriptive of purpose (semantic) or scale position (primitive)

### Primitive naming
Primitives describe WHAT the value is, not WHERE it's used.

```
color.{hue}.{scale}        → color.blue.500, color.neutral.100
spacing.{scale}             → spacing.1, spacing.2, spacing.4, spacing.8
fontSize.{scale}            → fontSize.xs, fontSize.sm, fontSize.base, fontSize.lg
fontWeight.{name}           → fontWeight.regular, fontWeight.medium, fontWeight.bold
fontFamily.{purpose}        → fontFamily.heading, fontFamily.body, fontFamily.mono
borderRadius.{scale}        → borderRadius.sm, borderRadius.md, borderRadius.lg, borderRadius.full
shadow.{scale}              → shadow.sm, shadow.md, shadow.lg
lineHeight.{scale}          → lineHeight.tight, lineHeight.normal, lineHeight.relaxed
letterSpacing.{scale}       → letterSpacing.tight, letterSpacing.normal, letterSpacing.wide
opacity.{scale}             → opacity.disabled, opacity.hover, opacity.overlay
```

### Colour scale convention
Use a 50-950 scale (matching Tailwind/MUI convention):
- 50: Lightest tint (backgrounds, subtle fills)
- 100-200: Light tints (hover states, borders)
- 300-400: Mid tones (secondary text, icons)
- 500: Base/reference value
- 600-700: Strong tones (primary text on light bg, active states)
- 800-900: Darkest shades (headings, high-contrast text)
- 950: Near-black (used sparingly)

### Semantic naming
Semantic tokens describe WHERE and WHY a value is used.

```
color.text.{variant}        → color.text.primary, color.text.secondary, color.text.disabled, color.text.inverse
color.surface.{variant}     → color.surface.default, color.surface.raised, color.surface.overlay
color.border.{variant}      → color.border.default, color.border.strong, color.border.subtle
color.interactive.{state}   → color.interactive.default, color.interactive.hover, color.interactive.active, color.interactive.disabled
color.feedback.{type}       → color.feedback.success, color.feedback.warning, color.feedback.error, color.feedback.info
spacing.component.{size}    → spacing.component.xs, spacing.component.sm, spacing.component.md, spacing.component.lg
spacing.layout.{size}       → spacing.layout.section, spacing.layout.page, spacing.layout.gutter
typography.{role}            → typography.display, typography.heading, typography.body, typography.caption, typography.label
```

### Component token naming
Component tokens are scoped to a specific component.

```
{component}.{property}.{state}
button.background.default
button.background.hover
button.background.active
button.background.disabled
button.text.default
button.text.disabled
button.border.default
button.border.focus
button.padding.horizontal
button.padding.vertical
button.borderRadius
card.background.default
card.border.default
card.padding
card.borderRadius
card.shadow
input.background.default
input.background.focus
input.border.default
input.border.error
input.border.focus
input.text.default
input.text.placeholder
```

## Alias rules

- Semantic tokens MUST reference primitives (never hardcode values)
- Component tokens MUST reference semantic tokens (never reference primitives directly)
- This creates the chain: component → semantic → primitive
- Exception: spacing and borderRadius component tokens may reference primitives directly when the semantic layer adds no value

```json
// CORRECT: component → semantic → primitive
"button.background.default": { "$value": "{color.interactive.default}" }
"color.interactive.default": { "$value": "{color.brand.primary}" }
"color.brand.primary": { "$value": "{color.blue.700}" }
"color.blue.700": { "$value": "#1B4965" }

// WRONG: component referencing a primitive directly
"button.background.default": { "$value": "{color.blue.700}" }
```

## Accessibility requirements

- All colour combinations used for text must meet WCAG 2.1 AA contrast ratio (4.5:1 for normal text, 3:1 for large text)
- Interactive elements must have a visible focus indicator
- Disabled states must still be distinguishable from enabled states
- When creating colour tokens, note the contrast ratio with common background colours in the `$description`

## File organisation

```
tokens/
├── primitives/
│   ├── colours.json       # All colour primitives (brand, neutral, feedback hues)
│   ├── typography.json    # Font families, sizes, weights, line heights
│   ├── spacing.json       # Spacing scale, border radius, sizing
│   └── effects.json       # Shadows, opacity values
├── semantic/
│   ├── colours.json       # Semantic colour mappings
│   ├── typography.json    # Typography role mappings
│   └── spacing.json       # Layout and component spacing
└── component/
    ├── button.json        # Button-specific tokens
    ├── input.json         # Input-specific tokens
    ├── card.json          # Card-specific tokens
    └── ...                # One file per component that needs specific tokens
```
