1# Product register
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3When design SERVES the product: app UIs, admin dashboards, settings panels, data tables, tools, authenticated surfaces, anything where the user is in a task.
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5## The product slop test
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7Not "would someone say AI made this." Familiarity is often a feature here. The test is: would a user fluent in the category's best tools (Linear, Figma, Notion, Raycast, Stripe come to mind) sit down and trust this interface, or pause at every subtly-off component?
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9Product UI's failure mode isn't flatness, it's strangeness without purpose: over-decorated buttons, mismatched form controls, gratuitous motion, display fonts where labels should be, invented affordances for standard tasks. The bar is earned familiarity. The tool should disappear into the task.
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11## Typography
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13- **System fonts are legitimate.** `-apple-system, BlinkMacSystemFont, "Segoe UI", system-ui, sans-serif` gives you native feel on every platform. Inter is the common cross-platform default for a reason.
14- **One family is often right.** Product UIs don't need display/body pairing. A well-tuned sans carries headings, buttons, labels, body, data.
15- **Fixed rem scale, not fluid.** Clamp-sized headings don't serve product UI. Users view at consistent DPI, and a fluid h1 that shrinks in a sidebar looks worse, not better.
16- **Tighter scale ratio.** 1.125–1.2 between steps is typical. More type elements here than on brand surfaces; exaggerated contrast creates noise.
17- **Line length still applies for prose** (65–75ch). Data and compact UI can run denser; tables at 120ch+ are fine.
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19## Color
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21Product defaults to Restrained. A single surface can earn Committed (a dashboard where one category color carries a report, an onboarding flow with a drenched welcome screen), but Restrained is the floor.
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23- State-rich semantic vocabulary: hover, focus, active, disabled, selected, loading, error, warning, success, info. Standardize these.
24- Accent color used for primary actions, current selection, and state indicators only, not decoration.
25- A second neutral layer for sidebars, toolbars, and panels (slightly cooler or warmer than the content surface).
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27## Layout
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29- Predictable grids. Consistency IS an affordance; users navigate faster when the structure is expected.
30- Familiar patterns are features. Standard navigation (top bar, side nav), breadcrumbs, tabs, and form layouts have established user expectations. Don't reinvent for flavor.
31- Responsive behavior is structural (collapse sidebar, responsive table, breakpoint-driven columns), not fluid typography.
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33## Components
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35Every interactive component has: default, hover, focus, active, disabled, loading, error. Don't ship with half of these.
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37- Skeleton states for loading, not spinners in the middle of content.
38- Empty states that teach the interface, not "nothing here."
39- Consistent affordances across the surface. Same button shape. Same form-control vocabulary. Same icon style.
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41## Motion
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43- 150–250 ms on most transitions. Users are in flow; don't make them wait for choreography.
44- Motion conveys state, not decoration. State change, feedback, loading, reveal: nothing else.
45- No orchestrated page-load sequences. Product loads into a task; users don't want to watch it load.
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47## Product bans (on top of the shared absolute bans)
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49- Decorative motion that doesn't convey state.
50- Inconsistent component vocabulary across screens. If the "save" button looks different in two places, one is wrong.
51- Display fonts in UI labels, buttons, data.
52- Reinventing standard affordances for flavor (custom scrollbars, weird form controls, non-standard modals).
53- Heavy color or full-saturation accents on inactive states.
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55## Product permissions
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57Product can afford things brand surfaces can't.
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59- System fonts and familiar sans defaults (Inter, SF Pro, system-ui stacks).
60- Standard navigation patterns: top bar + side nav, breadcrumbs, tabs, command palettes.
61- Density. Tables with many rows, panels with many labels, dense information when users need it.
62- Consistency over surprise. The same visual vocabulary screen to screen is a virtue; delight is saved for moments, not pages.
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