Design Md

DESIGN.md — Design System Source of Truth

DESIGN.md is an open format (repo: google-labs-code/design.md, package @google/design.md) for describing a visual identity to coding agents. It combines machine-readable design tokens (YAML front matter) with human-readable rationale (Markdown prose). Tokens are normative; prose provides application context.

When this skill loads, the design system stops being something the agent guesses at and becomes something the agent reads. Every sibling design skill in the frontend plugin should defer to DESIGN.md when it exists.

MANDATORY PREPARATION

The spec is alpha and under active development. Before any non-trivial authoring work, fetch the authoritative spec and linting rules:

npx @google/design.md@latest spec --rules

Treat that output as canonical. Do not paraphrase the schema from memory for high-stakes changes — re-verify.

Detection & Mode

Before acting, decide which of three modes you are in.

1. Consume mode — DESIGN.md exists at the project root or docs/DESIGN.md. Read it first, internalize ## Overview and ## Do's and Don'ts, and ground every downstream suggestion in its tokens.
2. Author mode — user asks to "create a design system", "write design tokens", "generate a style guide", or wants to seed one alongside a shadcn init.
3. Propose mode — neither file nor explicit ask, but the user is picking colors/typography from scratch. Use AskUserQuestion to ask whether to commit to a DESIGN.md before scattering ad-hoc hex values.

Detect with ls DESIGN.md docs/DESIGN.md 2>/dev/null or Glob("{DESIGN.md,docs/DESIGN.md,design/DESIGN.md}"). Do not assume.

Spec Essentials

Section order is fixed. Sections can be omitted, but the ones present must follow this order (the section-order lint rule is a warning):

YAML front matter schema (abbreviated — verify against spec --rules for edge cases):

---
version: alpha
name: <string>
description: <string>                   # optional
colors:
  <token-name>: "#RRGGBB"               # any CSS color (hex/named/rgb/hsl/oklch/color-mix); hex recommended, converted to sRGB for WCAG checks
typography:
  <token-name>:
    fontFamily: <string>
    fontSize: <Dimension>               # px | em | rem
    fontWeight: <number>                # 100..900
    lineHeight: <Dimension | number>    # unitless = multiplier of fontSize (preferred)
    letterSpacing: <Dimension>
    fontFeature: <string>               # optional, maps to font-feature-settings
    fontVariation: <string>             # optional, maps to font-variation-settings
rounded:
  <scale>: <Dimension>                  # sm, md, lg, xl, full, ...
spacing:
  <scale>: <Dimension | number>
components:
  <component>:
    backgroundColor: "{colors.primary}"  # references via {path.to.token}
    textColor: "{colors.on-primary}"
    typography: "{typography.body-md}"  # components may reference composite typography
    rounded: "{rounded.md}"
    padding: <Dimension>
    size|height|width: <Dimension>
---

Valid component properties: backgroundColor, textColor, typography, rounded, padding, size, height, width. Variants are expressed as sibling keys (button-primary, button-primary-hover, button-primary-active).

Recommended (non-normative) token names:

• Colors: primary, secondary, tertiary, neutral, surface, on-surface, error
• Typography: headline-display, headline-lg, headline-md, body-lg, body-md, body-sm, label-lg, label-md, label-sm
• Rounded: none, sm, md, lg, xl, full

CLI Workflow

All commands accept a file path or - for stdin. Default output is JSON, exit code 1 on error/regression.

lint — validate structure and token resolution

npx @google/design.md@latest lint DESIGN.md

The linter runs eight rules:

Fix error rows first. Surface contrast-ratio warnings to the user — promote them to ship blockers if the project commits to WCAG AA+.

diff — regression detection between two revisions

npx @google/design.md@latest diff DESIGN.md DESIGN.next.md

Exits 1 when the candidate has more errors or warnings than the baseline. Use before committing any token schema change.

export — emit consumable token shapes

npx @google/design.md@latest export --format tailwind DESIGN.md   # v3 theme.extend JSON
npx @google/design.md@latest export --format dtcg DESIGN.md       # W3C DTCG tokens.json

spec — inject spec into an agent prompt

npx @google/design.md@latest spec                     # full markdown spec
npx @google/design.md@latest spec --rules             # + lint rules table
npx @google/design.md@latest spec --rules-only        # only the rules table
npx @google/design.md@latest spec --format json       # programmatic

Programmatic API (when scripting)

import { lint } from '@google/design.md/linter';

const report = lint(markdownString);
report.findings;      // Finding[]
report.summary;       // { errors, warnings, info }
report.designSystem;  // parsed DesignSystemState

Tailwind v4 Adaptation (critical)

export --format tailwind emits Tailwind v3 shape (JS theme.extend object with colors, fontFamily, fontSize, borderRadius, spacing). The frontend plugin targets Tailwind v4 with CSS-first @theme { ... }. Do not drop the raw JSON into tailwind.config.*.

Apply this transform when emitting into app/globals.css (or wherever @theme lives):

Example:

@theme {
  --color-primary: #1a1c1e;
  --color-neutral: #f7f5f2;
  --font-h1: "Public Sans", sans-serif;
  --text-h1: 3rem;
  --text-h1--line-height: 1.1;
  --text-h1--letter-spacing: -0.02em;
  --radius-sm: 4px;
  --spacing-md: 16px;
}

For v3 projects, copy the JSON straight into theme.extend and stop.

Sibling Skill Integration

When DESIGN.md is present, it is the source of truth. Override heuristic defaults from other skills:

• frontend:impeccable — inject the ## Overview and ## Do's and Don'ts prose into the context-gathering protocol. Never suggest palettes that contradict defined tokens.
• frontend:impeccable (argument: colorize) — restrict new accents to the colors.* map. If a hue is genuinely missing, propose adding it to DESIGN.md (and the token name) rather than inlining raw hex.
• frontend:impeccable (argument: typeset) — pull from typography.* tokens directly. Surface missing-typography findings before suggesting fonts from scratch.
• frontend:impeccable (argument: audit) — run lint --format json as part of the audit. Include every error in the report; treat contrast-ratio warnings as blockers on AA-committed projects.
• frontend:impeccable (argument: critique) — cite ## Do's and Don'ts when flagging usability issues.
• frontend:web-design-guidelines — cross-reference contrast-ratio findings with the guideline rules.
• frontend:shadcn — map DESIGN.md components.button-primary.* onto shadcn's CSS variable contract (--primary, --primary-foreground, --radius). DESIGN.md exports provide the semantic variables that satisfy the shadcn rule "no raw bg-blue-500".

Authoring Flow

1. Use AskUserQuestion to collect: brand personality (2–3 adjectives), primary brand color, typography preference (serif / sans / geometric), target density (spacious / compact).
2. Draft YAML front matter with primary and neutral as minimum colors. Most sections break without neutral.
3. Write ## Overview first — it grounds every later token decision.
4. Fill ## Colors and ## Typography. Expand ## Components only once base tokens stabilize.
5. Run lint. Fix error rows before writing any implementation code.
6. Run export --format tailwind, apply the v4 transform above, and commit to the project's global stylesheet.
7. Run export --format dtcg if the project also feeds Figma variables or a separate token pipeline.

Consumption Flow

1. Read DESIGN.md in full. Internalize ## Overview and ## Do's and Don'ts.
2. Run lint --format json once at session start. Surface any error to the user before proceeding.
3. Reference tokens by name in prose suggestions ("use colors.tertiary for the CTA"). Let the implementation emit the matching Tailwind v4 variable (e.g., bg-[var(--color-tertiary)] or the project's mapped utility).
4. Never introduce raw hex / rem values that cannot be expressed as existing tokens. If a new token is needed, propose adding it to DESIGN.md and re-run lint.

Caveats

• Spec version is alpha. Re-check spec --rules if more than a week has passed since last use.
• export --format tailwind still targets v3. Apply the v4 transform above until upstream ships a v4 adapter.
• Linter WCAG findings are warnings by default — promote to errors when running frontend:impeccable (argument: audit) for AA+ commitments.
• No runtime dependency. All CLI invocations go via npx @google/design.md@latest. Do not add @google/design.md to dependencies or devDependencies.
• alpha status means token groups may gain or lose fields — treat unknown properties as warnings, not errors (matches the spec's "Consumer Behavior for Unknown Content" table).

References

• Spec (live): npx @google/design.md@latest spec
• Lint rules (live): npx @google/design.md@latest spec --rules-only
• Spec (cached): ./references/upstream-spec.md — pinned snapshot of upstream docs/spec.md, refreshed by frontend/scripts/sync-design-md.sh
• README (cached): ./references/upstream-README.md — CLI reference, token interop notes
• GitHub repo: https://github.com/google-labs-code/design.md
• Examples: https://github.com/google-labs-code/design.md/tree/main/examples — atmospheric-glass, paws-and-paths, totality-festival
• Launch blog: https://blog.google/innovation-and-ai/models-and-research/google-labs/stitch-design-md/