1. Title + How it works
penpot-build-screen turns a brief into a crafted, on-system screen; every mutation goes through
execute_code; validate visually with export_shape; read structure with
penpotUtils.shapeStructure (full tool surface: shared/penpot-mcp-tool-reference.md). It first
discovers the existing design system (tokens + components via penpot-foundations / the local
library), then builds the screen section by section inside flex Boards, binding tokens and reusing
components — never generating an entire screen in one call.
2. The One Rule That Matters Most
Reuse the system; build incrementally. Prefer existing components and semantic tokens over raw
shapes. Build one section, checkpoint with an export_shape, then continue. If no system exists,
bootstrap only a minimal one (hand off to penpot-foundations for anything substantial).
3. Penpot MCP Tool Reference
Full surface: shared/penpot-mcp-tool-reference.md. Key calls: penpot.createBoard()/addFlexLayout()
for the screen and sections; penpot.library.local.components + comp.instance() to reuse components;
shape.applyToken for token binding; export_shape('selection'|'page') at checkpoints.
4. Plugin API Essentials
Gotcha numbers refer to shared/plugin-api-gotchas.md.
- Screen and sections are Boards with flex layout; compose with append order + gaps + align/justify.
- Reuse components via
component.instance(); don't redraw system parts as raw shapes. - #3 text auto-sizing — set
growTypetoauto-width/auto-heightAFTER anyresize()(which forcesfixed). - #4 flex overrides child x/y — use
layoutChildfor stretch/margins. - Bind colors/spacing/radius/type to semantic tokens, never hardcoded.
- #11 every new Board is born with an OPAQUE WHITE fill — this skill's critical failure mode.
createBoard()shipsfills = [{ fillColor: "#FFFFFF", fillOpacity: 1 }]; left in place, a structural wrapper's square white corners poke out behind rounded children (radius looks broken), and layout boards keeping the literal white never flip in dark mode (no token, off-system). Fill policy: decide per board — a structural board (layout-only chrome: sections, rows, wrappers) getsboard.fills = []; a surface (screen bg, card, sheet, button) binds acolor.bg.*token, never a literal. Default layout containers to transparent (shared/modes-and-policies.md). - #13b exact font match —
penpot.fonts.all.find(f => f.name === "…");findByNameis a substring search. - #15 — set
layoutChild.*only AFTERappendChild;openPageis async (two-call protocol: create+open, then assertcurrentPage.idbefore anycreateBoard). - #16 — run
clearFlipafter every section (fill-sized children can come back withflipX = true; canonical helper inshared/visual-effects.md). - #17 —
await board.waitForLayoutUpdate()before reading geometry (replaces the sleep-100ms idiom). - #18 — image fills:
const img = await penpot.uploadMediaUrl(name, url); shape.fills = [{ fillOpacity: 1, fillImage: img }], verified in the next call — seeshared/visual-effects.md. - Verify unfamiliar signatures with
penpot_api_infofirst.
5. Token-Aware Brief Contract
- Context — product, audience, platform, brand mood.
- Objective — the single screen and its primary user goal.
- Inputs — content/sections, existing tokens & components, style profile, viewport size.
- Constraints — use existing components; on-grid spacing; semantic tokens only; forbidden patterns; none of the named tells in
shared/design-quality.md§7; with strict anti-slop on, none of the keys the direction step refused (shared/anti-slop.md§1). - Acceptance Criteria — clear hierarchy; 4px rhythm; AA contrast; reuses system; responsive intent stated; design-quality score ≥ 3 on all seven axes (
shared/design-quality.md§8) or the weak axes explicitly presented; with strict anti-slop on, slop score ≤ 35 (penpot-anti-slopdiagnose).
Act as a senior product/visual designer who makes deliberate aesthetic decisions, not generic ones.
6. Mandatory Workflow
Visual self-review (mandatory): before every ✋ checkpoint that shows visual work, run the export → look → fix loop from
shared/visual-self-review.md— export the unit you just built, inspect the image yourself against the checklist, fix visible defects (max 2 iterations), and present that same export with any remaining defects named.
Phase 0 — Discovery. high_level_overview; inventory tokens/components (scripts/setupOrReuseSystem.js); analyze the brief (references/01-brief-analysis.md); pick a style profile (references/02-style-profiles.md) and a named screen skeleton (shared/design-quality.md §5) — check the ledger for prior screens this session and apply the variety rule (differ on ≥ 1 axis, say which). Anti-slop opt-in: read the stored preference (penpot-anti-slop → scripts/antiSlopPrefs.js); if it is unset and the brief doesn't answer it, ask the question in shared/anti-slop.md §0 (user's language, once per file) and store the answer. When it is on, run the direction step (penpot-anti-slop references/02-direction-playbook.md) before choosing profile and skeleton, and fold its refused keys into the Constraints. ✋ Checkpoint: confirm brief + style + skeleton + section list (+ the direction block when strict mode is on).
Phase 1 — Frame. Create the screen Board with scripts/createScreenFrame.js (idempotent; returns ids; binds bg/gap/padding tokens). Set viewport size. ✋ Checkpoint.
Phase 2..N — Sections. Build each section as a tokenized flex Board reusing components (scripts/buildSection.js). One section per execute_code call. ✋ Checkpoint after each (export_shape).
Phase N+1 — Assemble & critique. scripts/assembleScreen.js composes sections; scripts/auditScreenQuality.js checks layout coverage (every board has flex/grid), token binding, on-grid spacing, naming. A non-empty boardsWithoutLayout fails the gate — add a layout to each flagged board before reporting done. Then run the scored critique (references/05-critique-framework.md): score the final export 1–5 on the seven axes of shared/design-quality.md §8; any axis < 3 → targeted revision (max 2 passes), then emit the design-quality report (Markdown + JSON per shared/report-schemas/design-quality-report.schema.json, mirrored to the ledger). Strict mode on: run penpot-anti-slop diagnose on the screen board and include its slop score in the report (it feeds the distinctiveness axis); outside a workflow, a score > 35 means presenting its top fixes, not declaring done. Report.
7. Critical Rules
- Flex by default — every container is a layout Board. The instant you create a Board, give it a
flex (
addFlexLayout()) or grid (addGridLayout()) layout before appending children — the screen root, every section, AND every nested grouping (card, row, list, stat cluster, form field, button group). NEVER arrange UI elements with absolutex/y, and NEVER use a plain Group to lay out UI. A Board without a layout is a bug; the Phase N+1 audit (boardsWithoutLayout) fails the build if any exist. - Reuse existing components before creating raw shapes.
- Bind to semantic tokens; never hardcode color/spacing/radius/type.
- One section per call; checkpoint with
export_shape. - All spacing on the 4px grid; consistent rhythm.
- Don't bootstrap a full design system here — hand off to
penpot-foundations. - State responsive intent (sizing: fill/auto/fix) explicitly.
8. Domain Architecture
A screen = a root flex Board (column) → section Boards (each its own flex) → component instances + tokenized primitives. Composition follows a clear visual hierarchy: primary action prominent, content grouped, whitespace on the spacing scale, type from the semantic type tokens.
9. Modes & Policies
Default review. Geometry/layout changes always require a checkpoint (shared/modes-and-policies.md).
10. State Management
Ledger under RUN_ID: phase, screenBoardId, sections:[{name,id,done}], styleProfile, skeleton, designQuality (the §8 report object), antiSlop (pref, direction, reports[] — when strict mode is on). The opt-in itself is file-wide plugin data penpot-ai → prefs.antiSlop. Resume by re-reading structure.
11. User Checkpoints
| After phase | Artifacts | Ask |
|---|---|---|
| 0 (pref unset) | the anti-slop opt-in question (shared/anti-slop.md §0) |
Avoid the generic-AI look? |
| 0 | brief + style + skeleton + sections (+ direction block if strict) | Approve direction? |
| 1 | empty frame export_shape |
Approve frame/viewport? |
| each section | section export_shape |
Approve section? |
| assemble | full screen export_shape + scored critique (7 axes) |
Approve / iterate? |
12. Naming Conventions
shared/naming-conventions.md: layers semantic HTML (header, main, section, nav, button); screen Board named for the view (Dashboard).
13. Anti-Rationalization Table
| Excuse | Why it's wrong | Countermeasure (halt) |
|---|---|---|
| "I'll draw a quick button instead of using the component." | Raw shapes drift from the system. | Instantiate the existing component; reuse beats reinvention. |
| "Hardcode this spacing/color, faster." | Breaks rhythm/theming/governance. | Bind to semantic tokens; snap spacing to 4px. |
| "Generate the whole screen in one go." | One-shot output is generic and unauditable. | Build section by section with checkpoints. |
| "Centered cards + generic gradient looks fine." | Distributive convergence → bland, off-brand UI. | Apply a deliberate style profile; justify aesthetic choices. |
| "I'll skip the anti-slop question, the user is busy." | Strict mode is the user's choice; guessing either way is wrong. | Read prefs.antiSlop; unset → ask once (shared/anti-slop.md §0). |
| "I'll set up tokens here real quick." | Foundations belong in their skill. | Hand off to penpot-foundations for anything beyond trivial. |
| "I'll just position these with x/y, it's faster." | Absolute coords don't resize, reflow, or theme; off-system. | Wrap them in a flex/grid Board; order by append + gaps/align. |
| "A plain Group is enough to bunch these together." | Groups don't lay out — they only bound. | Use a Board with addFlexLayout(); the audit flags layout-less boards. |
| "This little container doesn't need a layout." | Every UI container needs one for rhythm + responsiveness. | Add flex/grid before appending children — no exceptions. |
14. Helper Code Snippets
// Screen frame (Phase 1)
const screen = penpot.createBoard();
screen.name = "Dashboard";
screen.resize(1440, 1024);
const flex = screen.addFlexLayout();
flex.dir = "column";
flex.horizontalSizing = "fix"; flex.verticalSizing = "auto";
penpot.currentPage.root.appendChild(screen); // append first (#7); layoutChild only after append (#15)
// SPACING: bind tokens, never literals (#8: padding tokens bind on ≥ 2.17; numeric mirror + ledger exception otherwise)
const gap = penpotUtils.findTokenByName("spacing.24");
if (gap) screen.applyToken(gap, ["rowGap"]); else flex.rowGap = 24;
const pad = penpotUtils.findTokenByName("spacing.32");
const FLEX_PROP = { paddingTop: "topPadding", paddingBottom: "bottomPadding", paddingLeft: "leftPadding", paddingRight: "rightPadding" };
for (const side of Object.keys(FLEX_PROP)) {
try { if (!pad) throw new Error("no token"); screen.applyToken(pad, [side]); }
catch (e) { flex[FLEX_PROP[side]] = pad ? Number(pad.resolvedValue) : 32; } // record { kind: "padding-mirrors-token" } in the ledger
}
// FILL POLICY (gotchas #11): the screen root is THE one surface — bind its bg to a token so it flips in
// dark mode. Every section nested inside stays transparent (buildSection.js clears their default white).
screen.fills = []; // drop Penpot's default opaque #FFFFFF
const bg = penpotUtils.findTokenByName("color.bg.default");
if (bg) screen.applyToken(bg, ["fill"]); // bound surface, not a literal
storage.bs = { screenBoardId: screen.id };
return { screen: screen.id, bgBound: !!bg, gapBound: !!gap, padBound: !!pad };
15. Reference Resources
penpot_api_info('Board'),penpot_api_info('LibraryComponent'),penpot_api_info('Text').
16. Supporting Files
references/: 01-brief-analysis.md, 02-style-profiles.md, 03-layout-composition.md, 04-component-recipes.md, 05-critique-framework.md, 06-anti-rationalization.md, 07-error-recovery.md; effects, image placeholders, gradients: shared/visual-effects.md.
scripts/: setupOrReuseSystem.js, createScreenFrame.js (Phase 1 frame: idempotent, token-bound bg/gap/padding, ledger), buildSection.js, assembleScreen.js, auditScreenQuality.js.
Doctrine paths. shared/… and policies/… resolve inside this bundle in native installs (vendored by the installer); in a Claude Code plugin install they live at the plugin root — ${CLAUDE_PLUGIN_ROOT}/shared/…, two directories up from this file.