Designkit

designkit

A design system that lives in someone's head, or in Figma, is invisible to the agent writing the UI. DESIGN.md is what the ecosystem converged on instead: an open format from Google Labs (Apache-2.0, google-labs-code/design.md) that pairs machine-readable design tokens in YAML front matter with human-readable rationale in prose. It is deliberately the design counterpart to the agent instruction files coding agents already read (CLAUDE.md and its equivalents), a persistent contract in the repo root that survives sessions, and that any DESIGN.md-aware agent reads.

designkit does the half the ecosystem left empty. Every other tool hands you a design system from somewhere else, whether a file reverse-engineered from Stripe or a palette retrieved from a product-type lookup table. designkit derives yours from the UI you already shipped, and tells you later when it has gone stale.

That makes the grounding rule the whole skill: every token must be a value that appears in your codebase. Clustering forty near-identical greys into a scale is derivation. Picking a nicer neighbouring hex because it rounds better is invention, and it is the one thing designkit never does.

What designkit is not

• Not a UI generator. It records the system; it writes no components, no pages, no application CSS. A skill that both defines the taste and applies it can't be held to the grounding rule.
• Not a taste library. It ships no palettes, no font pairings, no style catalog. If your project has no design system, designkit proposes one from your own values or says it can't; it never imports someone else's.
• Not a spec implementation. Linting, contrast checking, token export, and the schema itself belong to the official CLI. designkit shells out and reports; it is not a second, worse implementation.
• Not a design critique. Whether the system is any good is a human's call. designkit reports what is there, including when what's there is a mess.
• Not the glossary or the decision log. Domain vocabulary and architecture decisions belong elsewhere; a design token is neither.

When this fires

• init. "Write a DESIGN.md", "document our design system", "we have no design tokens", "what colors does this project actually use". Derives the file from the codebase.
• update. "The design system changed", "update DESIGN.md", or a design pass right after UI work lands. Applies what the code now says.
• audit. "Is our DESIGN.md still accurate", "check the design system against the code", "what's drifted". Read-only sweep. Writes nothing, ever.

If no mode is clear, ask. audit is free and init rewrites the project's design contract; never guess between them.

The artifact

DESIGN.md lives at the repo root. That's the spec's convention and how DESIGN.md-aware tools discover it, not docs/, however tempting the tidiness.

The token schema

Front matter opens with a line of exactly --- and closes the same way. This is the alpha schema as captured on 2026-08-06; prefer reading it live when the CLI is available, because the format is explicitly still moving.

version: <string>          # optional, current: "alpha"
name: <string>
description: <string>      # optional
omitted: <string[] | OmittedSection[]>   # optional; sections deliberately excluded
colors:
  <token-name>: <Color>            # "#1A1C1E", "oklch(62% 0.18 250)", CSS named
typography:
  <token-name>: <Typography>       # fontFamily, fontSize, fontWeight, lineHeight,
                                   # letterSpacing, fontFeature, fontVariation
rounded:
  <scale-level>: <Dimension>       # 4px, 0.5rem, 9999px
spacing:
  <scale-level>: <Dimension | number>
components:
  <component-name>:
    <token-name>: <string | token reference>   # "{colors.primary}"

Values cross-reference with {path.to.token} syntax. Prefer a reference over a repeated literal, because an unreferenced token trips orphaned-tokens, and a duplicated literal is how a system drifts.

Recommended token names (non-normative, but follow them unless the project already has its own vocabulary): 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.

The sections

Eight canonical ## headings, in this order. Out-of-order sections trip section-order; a duplicate heading is a hard error that rejects the file.

Two further sections are permitted after Do's and Don'ts, because the spec preserves unknown headings without error: ## Motion and ## Dark Mode. Both are prose only, and the reason below is not a stylistic preference.

Voice belongs in Do's and Don'ts rather than a section of its own. Rules about the strings on screen ("errors name the fix, not the failure") are guardrails, and the spec already has a section for guardrails.

What never goes in YAML

Verified by running the linter, not inferred from the docs. Two shapes look reasonable and both produce warnings on a file you'd otherwise call clean:

The complete set of valid component sub-tokens is backgroundColor, textColor, typography, rounded, padding, size, height, width. There is no duration, no easing, no border, no gap. Anything else warns.

So motion has no token home anywhere in the schema. Durations and easing curves are prose, and that's the honest representation until the spec grows a place for them.

What is token-legal is interaction state, through the related-key pattern the spec defines: button-primary, button-primary-hover, button-primary-active. Extract those as real component entries. Never invent a custom key to hold a state the pattern already expresses.

The stamp

Every file designkit writes ends with one visible line, after the last section:

_Extracted from `main`@`a1b2c3d` on 2026-08-06._

Both halves earn their place: audit recovers the baseline with git show <sha>:DESIGN.md while the SHA is reachable, and falls back to the date once a squash-merge has orphaned it. An HTML comment would be invisible in every renderer, which is exactly how a stale file comes to read as current.

A file with no stamp was written by a human. Adopt it, work with it, never silently claim it, and say plainly that you're editing a file designkit didn't author.

The CLI is the source of truth

The format is at version alpha and openly under active development. Hardcoding the schema into a skill is how the skill becomes confidently wrong, so read the spec at run time and treat the summary above as a dated fallback:

Exit codes: 0 success, 1 errors or regressions, 2 file read failure. On Windows PowerShell use the designmd alias, because the .md file association hijacks the other form.

The eleven lint rules run on every file: broken-ref (error), contrast-ratio, orphaned-tokens, missing-primary, missing-typography, section-order, unknown-key, token-like-ignored (warnings), and token-summary, missing-sections, omitted-rules (info). contrast-ratio already enforces WCAG AA at 4.5:1, so never write your own contrast math.

The extraction engine

One engine, shared by all three modes. init writes its output, update diffs and applies it, audit diffs and reports it. There is no manifest of watched paths to maintain, and therefore no change that goes unnoticed because a glob failed to cover it.

Find the token home

First rung that matches, and say which one matched before writing anything:

Derive from usage, not declarations

A declared token nobody uses is not the design system; forty hardcoded hexes are. Read both:

• every color literal in stylesheets, templates, and components, meaning hex, rgb(), hsl(), oklch(), and named colors
• the font sizes, weights, and line heights actually applied
• the padding, margin, and gap values that recur
• corner radii and shadows in use
• the interaction states actually styled: :hover, :focus-visible, :active, disabled, and their framework equivalents
• dark mode: grep .dark, prefers-color-scheme, dark: variants, [data-theme]

Count occurrences. A value used ninety times and a value used once are not equally part of the system, and the counts are what make the next part defensible.

Classify every token

Each token carries one of three states, and the classification is shown at the consent gate:

omitted is a feature, not a failure. The field exists precisely to declare deliberate exclusions and to suppress missing-section warnings. A DESIGN.md that honestly omits elevation beats one that invents a shadow scale.

When there's no system

The likeliest real input: hundreds of hardcoded values, no token home, no consistency. designkit clusters and proposes. It does not refuse, and it does not fall through to an interview when the taste is already on screen, just messily.

The proposal is bound by the grounding rule: every proposed token is a value that occurs in the code. Cluster near-duplicates, choose the most-used member of each cluster as the representative, and list the members it absorbs. Never emit a value the codebase has never contained.

Tune the cluster threshold to the project and state the threshold you used, because it's a judgment call, and an unstated one is unreviewable. Perceptual distance for color, nearest-step for spacing and type. When a cluster is too loose to call one system, split it rather than forcing a merge, and say so.

Show the work

Before writing anything, emit a disposable swatch sheet: a plain HTML page of color chips, type specimens, spacing bars, and radii, each labelled with its token name, its state, and the values it absorbed. Reviewing "forty greys became six" as a YAML diff is not realistic; as swatches it takes seconds.

This is review scaffolding, not a deliverable. Write it to a gitignored scratch path, add that path to .gitignore if it isn't covered, name it in the consent ask, and don't keep it. It is emphatically not the generated UI this skill refuses to write; it's a proof sheet for a decision.

Mode: init

1. Ground it

Run the extraction engine. Name the rung that matched, the number of distinct values found per category, and the dark-mode verdict, before proposing anything.

2. Interview only when there's nothing to read

No UI in the repo means nothing to extract. Ask for the essentials (brand intent, an existing palette, type preferences) and say plainly in the report and in the file's Overview that the result is proposed, not extracted. Anything still unknown is omitted.

3. Propose, and gate on it

Show the swatch sheet plus the extracted / consolidated / omitted breakdown, the cluster threshold, and every inconsistency found. This is the gate that matters, because the user accepts, trims, or redirects before a file exists.

4. Write, stamp, validate

Write DESIGN.md at the repo root, append the stamp, then run lint and report its findings verbatim, including any that remain. A warning you chose to accept is reported as accepted, never suppressed.

5. Hand off

Write every hand-off in this skill in the procedural register: one instruction per sentence, active voice, present tense, no metaphor.

What changed. Report the file created, the rung that matched, how many tokens landed in each state, and what was omitted.

Where it landed. Give DESIGN.md at the repo root, the swatch sheet's scratch path (and that it's disposable), and the lint result.

Next. Read the file. It's a claim about your project's visual identity and it's the one thing here a human should actually check. Then commit it with commitkit when installed, otherwise git add DESIGN.md and commit. If the project has a token home and the file's values differ from it, token sync is the follow-up; if it doesn't, there is nothing to sync and no next step to invent.

Mode: update

1. Resolve the target

Uncommitted working-tree changes first (git status --porcelain non-empty → git diff HEAD, plus untracked files, which git diff never shows). Otherwise the branch diff against the base ref, from gitkit when it's installed, else the repo's default branch via gh repo view --json defaultBranchRef. Never assume main. Say which target you chose in one line.

2. Re-extract and diff

Run the engine against the current code and diff its result against the committed DESIGN.md. Where the stamped SHA is still reachable, also run npx @google/design.md diff <baseline> <current> for the structured token-level comparison.

3. Apply, with restraint

A changed brand color edits the color token. It does not regenerate the file. State which sections are affected and which are deliberately untouched before editing, because the untouched list is the load-bearing half, and it's what shows the skill knew what it was leaving alone.

Edits to existing tokens and prose land directly; they're bounded by that restraint and land in a reviewable diff. New sections and deletions are consent-gated. A skill that rewrites a design system because one button changed is worse than no skill.

4. Re-stamp and validate

Re-stamp with the current ref and SHA, run lint, report.

5. Hand off

What changed. Report tokens edited (one line each, naming the value that moved), sections proposed and their verdict, and sections deliberately untouched.

Where it landed. Give DESIGN.md, and the lint result.

Next. Run commitkit, then prkit if this is branch work (otherwise git commit and gh pr create). The design system lands in the same commit as the UI change that moved it; that's the point of keeping it in the repo.

Mode: audit

Read-only. Writes nothing, ever. It reports and routes; fixing is a separate invocation, deliberately.

Three checks:

• Lint. Run npx @google/design.md lint, findings reported as-is.
• Drift. The check only designkit can do, because the linter validates the file against itself and has no view of the codebase. Two directions: tokens in the file that no longer appear in the code, and values in the code that no token covers.
• Baseline. Run npx @google/design.md diff against git show <stamped-sha>:DESIGN.md, when the SHA is reachable.

The report

Open with a coverage line, naming how many files were scanned and how many skipped, because an audit that silently covered a fraction of the UI reads exactly like a clean bill of health. Then crown one next move.

Hand off

What changed. Nothing. Say it outright; a reader should never have to wonder whether a read-only mode wrote something.

Where it landed. Inline in this reply. There's no audit artifact by default; offer to save one only if asked.

Next. Crown the single worst drift and route it to update, or to init when the file is missing rather than wrong. "Nothing has drifted" is a valid, stated result, so say the system is current and stop.

Token sync

On consent, and only where a token home already exists. designkit never introduces a token system to a project that doesn't have one, because that's a build-tooling decision, not a documentation one.

The seam is transformation, not framework: if the official exporter already emits the shape, designkit writes it; if it needs real conversion, designkit emits DTCG and names the tool. Hand-rolled converters drift the moment either format moves.

Degrade loudly

No npx, no network, or no CLI is a normal condition, not an error. Extract and write from the fallback schema above, skip lint and export, and name the gap in the same breath as the result:

Wrote DESIGN.md (12 colors, 6 type styles). lint not run, because no npx was available. Schema from the bundled alpha fallback captured 2026-08-06.

Never claim validation that didn't happen. A file reported as clean when nothing checked it is worse than a file reported as unchecked.

No filesystem at all (a browser-based agent)? Print the finished DESIGN.md as a fenced block labelled with its path, describe the swatch sheet rather than writing it, and name the commands the user should run themselves.

Notes

• The grounding rule outranks completeness. A sparse, honest file beats a full, invented one. When the choice is between omitting a scale and guessing at it, omit and say so.
• Consent by operation. The init proposal, new sections, deletions, and any token sync all ask. Edits to existing tokens in update don't, because they're bounded by the restraint rule and land in a reviewable diff. audit asks for nothing, because it changes nothing.
• Report warnings, never suppress them. If a lint warning survives, it goes in the report with the reason it was accepted.
• Existing project convention wins. A repo with its own token names, its own file location, or its own design-doc layout gets followed, and designkit says which convention it followed.
• The spec is alpha. Sections, schema keys, and rules move. Read them from the CLI at run time; when the bundled fallback is what ran, say so.
• Prose is for rationale, tokens are for values. An agent needs the hex, not the story behind the hex. Keep prose to what a token can't carry: intent, and when not to reach for something. For a general pass over that prose, use humankit when installed.