Design Language Doc (DESIGN.md)

You are creating this repository's design-language contract: a root DESIGN.md that tells agents and humans exactly how UI is built here, plus a portable frontend-design craft skill. The doc is downstream of the code — you describe the design language that exists, or propose one with user approval. You never invent a design language and present it as fact, and you never restyle existing UI to match a doc.

Goal

1. Root DESIGN.md — the repo's design language, written from evidence, citing real files and tokens
2. .agents/skills/frontend-design/SKILL.md — portable craft doctrine (typography, surfaces, motion) that applies to any repo
3. A link from AGENTS.md so agents find the design language within one hop

Reference templates

Phase 0: Audit, then classify (before writing anything)

Config first. If docs/agents/skills-config.md exists, read it before anything else — it may already record the classification mode and, for Mode C, a settled aesthetic direction from the setup interview. Never re-ask a decision recorded there. If the file does not exist (this skill was invoked directly), classify and settle decisions yourself as described below.

Gather evidence. Every claim in DESIGN.md must trace back to something you saw here:

• package.json: framework, UI libraries (react/vue/svelte, tailwind, shadcn, radix/base-ui, motion/framer-motion, lucide, fonts packages)
• Token layer: globals.css / tailwind.config.* / theme files — CSS variables, @theme blocks, custom utilities (shadows, radii, animations)
• Fonts: how they're loaded (next/font, @font-face, link tags), which families, which roles
• Component system: components/ui/, shared primitives, variant patterns (cva, variants props)
• Motion: keyframes, transition utilities, motion-library usage, prefers-reduced-motion handling
• The 3–5 most polished surfaces in the app — these define the actual design language, whatever the tokens claim
• Existing design docs: DESIGN.md, docs/design*, brand guidelines, Figma links in READMEs, design-related Cursor rules or agent docs

Then classify the repo into exactly one mode:

Mode A — Document (established design language, no design doc)

The repo has consistent tokens, deliberate font choices, a component system, recurring motifs. Your job is extraction: write DESIGN.md describing what exists, citing the files that prove it. Nothing about the actual design changes. Where the codebase is internally inconsistent, document the dominant/most-recent pattern and note the deviation — do not resolve it by fiat.

Mode B — Merge (design docs already exist)

A DESIGN.md, brand guide, or design-related rules already exist. Merge, never regenerate: preserve every unique local rule, deduplicate against the template structure, keep one source of truth, and leave pointers behind if you consolidate scattered docs. If existing docs contradict the code, flag the contradiction to the user instead of silently picking a side.

Mode C — Propose (greenfield, no coherent design language)

No established language exists. Choosing an aesthetic direction is a user-owned decision, not an evidence question. Run the decisions through the frontier-interview skill: aesthetic direction and tone is the root decision; font pairing (display + body), color approach and the accent budget, elevation strategy, and motion approach are downstream of it. Offer 2–3 distinct directions as the recommended answers where the product context supports them. Then write a one-page proposal to docs/plans/design-language.md (or PLAN.md if the repo has no docs/plans/) from the settled answers. Stop and get user approval of the proposal before writing DESIGN.md. After approval, write the full doc from the approved proposal.

Deliverables

DESIGN.md                              # root design-language contract (living document)
.agents/
  skills/
    frontend-design/SKILL.md           # portable craft doctrine (references/skill-frontend-design.md)
docs/
  plans/
    design-language.md                 # Mode C only: the approved proposal

Plus one edit: add - [Design Language](DESIGN.md) to the Quick Links in AGENTS.md (create the section if the repo has an AGENTS.md without it; skip if there is no AGENTS.md).

Process (in order)

1. Phase 0 audit and classification (checklist above)
2. Mode C only: interview (per the frontier-interview skill), write the proposal, present it, and wait for approval
3. Write DESIGN.md using references/design-md-template.md as structure — filled from evidence (Modes A/B) or the approved proposal (Mode C)
4. Create .agents/skills/frontend-design/SKILL.md verbatim from references/skill-frontend-design.md (stripping the template preamble), unless the repo already has an equivalent craft skill — then skip it
5. Link DESIGN.md from AGENTS.md Quick Links
6. Run the verification pass below
7. Report: mode chosen and why, files created, contradictions found between docs and code, rules preserved from pre-existing docs

Writing rules for DESIGN.md

• Cite real files. Every token, utility, font, and component pattern named in the doc must link to the file that defines it
• Name the budgets. Great design languages are mostly restraint — make limits explicit ("one accent pairing per view", "at most one display-font moment per page"), because agents follow budgets better than vibes
• Include the one-liner. A blockquote near the top that compresses the whole language into one paragraph an agent can carry to another surface
• End with a per-page checklist of verifiable items, phrased so an agent can self-review against them
• Sizes over adjectives. "rounded-3xl cards, rounded-full CTAs" beats "generously rounded"
• Semantic tokens over hardcoded values everywhere the repo's token system reaches; name the sanctioned exceptions explicitly

Constraints

• Never restyle existing components to match DESIGN.md. The doc describes or proposes; it does not authorize a refactor. If the user wants the UI brought in line with the doc, that is a separate, explicit task
• In Modes A and B, do not "improve" the design language while documenting it — record improvement ideas at the end under a clearly-marked "Open questions" section instead
• Do not copy another product's design language (fonts, palettes, motifs) into DESIGN.md unless verified in THIS repo or approved in the Mode C proposal
• Prefer an accurate short doc over an impressive long one — an agent that trusts a wrong design doc produces confidently wrong UI
• Match the repo's markdown tone and formatting

Re-runs, stamps, and owned files

• Stamp every emitted artifact. The first line of every file this skill creates (DESIGN.md, the proposal doc, the emitted frontend-design skill) is <!-- generated by design-md v<version> --> (version from this skill's frontmatter). In emitted SKILL.md files, place the stamp immediately after the frontmatter.
• Ownership by stamp. On re-run, a file carrying this skill's stamp may be updated — but rules the user added or edited since are preserved, never regenerated away. A file without this skill's stamp is not yours (a hand-written DESIGN.md is Mode B by definition): merge into it in place; never overwrite it and never create a duplicate beside it.
• The AGENTS.md edit is idempotent. The Quick Links line is a single-line insertion into a file this skill doesn't own: check for presence, add if absent, touch nothing else.

Verification pass (required before finishing)

• Every file path referenced in DESIGN.md resolves to an existing file
• Every token, utility class, and font named in the doc exists in the codebase (grep for it)
• Modes A/B: no rule in the doc contradicts what the most polished surfaces actually do
• Mode B: every unique rule from the pre-existing docs survived the merge (diff them)
• Mode C: the doc matches the approved proposal; the proposal file exists in docs/plans/
• The AGENTS.md link resolves
• The checklist at the end of DESIGN.md contains only items an agent can verify from code
• Every emitted file carries this skill's generation stamp; no file without the stamp was overwritten

Done when

• An agent building UI in this repo can answer "what fonts, what tokens, what radii, what shadows, what motion?" from DESIGN.md alone, one hop from AGENTS.md
• The user's existing design decisions are intact — nothing was overwritten, and any new direction was explicitly approved
• The portable frontend-design craft skill is installed
• Every doc statement is evidence-backed (or approval-backed) and the verification pass is clean