Web UI Best Practices

When invoked generally, apply these opinionated constraints for building better interfaces and for any UI work in this conversation.

When invoked with a file specified (i.e.

web-ui-best-practices <file>

), review the file against all constraints below and output:

violations (quote the exact line/snippet)
why it matters (1 short sentence)
a concrete fix (code-level suggestion)

Stack

MUST use Tailwind CSS defaults unless custom values already exist or are explicitly requested
MUST use
```
motion/react
```
(formerly
```
framer-motion
```
) when JavaScript animation is required
SHOULD use
```
tw-animate-css
```
for entrance and micro-animations in Tailwind CSS
MUST use
```
cn
```
utility (
```
clsx
```
+
```
tailwind-merge
```
) for class logic

Components

MUST use accessible component primitives for anything with keyboard or focus behavior (
```
Base UI
```
,
```
Radix
```
,
```
React-Aria
```
)
MUST use the project’s existing component primitives first
NEVER mix primitive systems within the same interaction surface
SHOULD prefer
```
Base UI
```
for new primitives if compatible with the stack
MUST add an
```
aria-label
```
to icon-only buttons
NEVER rebuild keyboard or focus behavior by hand unless explicitly requested

Interaction

MUST use an
```
AlertDialog
```
for destructive or irreversible actions
SHOULD use structural skeletons for loading states
NEVER use
```
h-screen
```
, use
```
h-dvh
```
MUST show errors next to where the action happens
NEVER block paste in
```
input
```
or
```
textarea
```
elements

Navigation & State

SHOULD reflect UI state in the URL (filters, tabs, pagination, expanded panels via query params)
MUST use
```
<a>
```
/
```
<Link>
```
for navigation (Cmd/Ctrl+click and middle-click should work)
SHOULD deep-link stateful UI (if it uses
```
useState
```
, consider URL sync via
```
nuqs
```
or similar)
MUST require confirmation or undo window for destructive actions (never immediate)

Touch & Interaction

SHOULD set
```
touch-action: manipulation
```
on tappable controls (prevents double-tap zoom delay)
SHOULD set
```
-webkit-tap-highlight-color
```
intentionally
MUST use
```
overscroll-behavior: contain
```
in modals/drawers/sheets
SHOULD during drag: disable text selection,
```
inert
```
on dragged elements
SHOULD use
```
autoFocus
```
sparingly (desktop only, single primary input; avoid on mobile)

Animation

NEVER add animation unless it is explicitly requested
MUST animate only compositor props (
```
transform
```
,
```
opacity
```
)
NEVER animate layout properties (
```
width
```
,
```
height
```
,
```
top
```
,
```
left
```
,
```
margin
```
,
```
padding
```
)
SHOULD avoid animating paint properties (
```
background
```
,
```
color
```
) except for small, local UI (text, icons)
SHOULD use
```
ease-out
```
on entrance
NEVER exceed
```
200ms
```
for interaction feedback
MUST pause looping animations when off-screen
SHOULD respect
```
prefers-reduced-motion
```
NEVER introduce custom easing curves unless explicitly requested
SHOULD avoid animating large images or full-screen surfaces
SHOULD never
```
transition: all
```
—list properties explicitly
SHOULD set correct
```
transform-origin
```
SHOULD have animations be interruptible—respond to user input mid-animation

Typography

MUST use
```
text-balance
```
for headings and
```
text-pretty
```
for body/paragraphs
MUST use
```
tabular-nums
```
for data
SHOULD use
```
truncate
```
or
```
line-clamp
```
for dense UI
NEVER modify
```
letter-spacing
```
(
```
tracking-*
```
) unless explicitly requested
SHOULD use
```
…
```
not
```
...
```
SHOULD use curly quotes
```
"
```
```
"
```
not straight
```
"
```
SHOULD have non-breaking spaces:
```
10&nbsp;MB
```
,
```
⌘&nbsp;K
```
, brand names
SHOULD have loading states end with
```
…
```
:
```
"Loading…"
```
,
```
"Saving…"
```
SHOULD use
```
font-variant-numeric: tabular-nums
```
for number columns/comparisons
SHOULD have flex children need
```
min-w-0
```
to allow text truncation
SHOULD handle empty states—don't render broken UI for empty strings/arrays
SHOULD consider that user-generated input fields may have short, average, and very long inputs

Layout

MUST use a fixed
```
z-index
```
scale (no arbitrary
```
z-*
```
)
SHOULD use
```
size-*
```
for square elements instead of
```
w-*
```
+
```
h-*
```

Safe Areas & Layout

MUST respect
```
env(safe-area-inset-*)
```
for full-bleed layouts and fixed elements on notched devices
SHOULD avoid unwanted scrollbars (use
```
overflow-x-hidden
```
on containers and fix overflow at the source)
SHOULD prefer flex/grid over JS measurement for layout

Dark Mode & Theming

MUST set
```
color-scheme: dark
```
on
```
<html>
```
for dark themes (fixes scrollbars and native inputs)
SHOULD set
```
<meta name="theme-color">
```
to match the page background
SHOULD set explicit
```
background-color
```
and
```
color
```
on native
```
<select>
```
(Windows dark mode)

Locale & i18n

MUST use
```
Intl.DateTimeFormat
```
(no hardcoded date/time formats)
MUST use
```
Intl.NumberFormat
```
(no hardcoded number/currency formats)
SHOULD detect language via
```
Accept-Language
```
/
```
navigator.languages
```
, not IP

Hydration Safety

MUST provide
```
onChange
```
for inputs with
```
value
```
(or use
```
defaultValue
```
for uncontrolled inputs)
MUST guard date/time rendering against hydration mismatches (server vs client)
SHOULD use
```
suppressHydrationWarning
```
only where truly needed

Hover & Interactive States

SHOULD provide
```
hover:
```
states for buttons/links (visual feedback)
SHOULD increase contrast for interactive states (hover/active/focus more prominent than rest)

Images

MUST set explicit
```
width
```
and
```
height
```
on
```
<img>
```
(prevents CLS)
SHOULD set
```
loading="lazy"
```
for below-fold images
SHOULD set
```
priority
```
or
```
fetchpriority="high"
```
for above-fold critical images

Performance

NEVER animate large
```
blur()
```
or
```
backdrop-filter
```
surfaces
NEVER apply
```
will-change
```
outside an active animation
NEVER use
```
useEffect
```
for anything that can be expressed as render logic
SHOULD virtualize large lists (>50 items) (e.g.
```
virtua
```
or
```
content-visibility: auto
```
where appropriate)

MUST avoid layout reads during render (

getBoundingClientRect

offsetHeight

offsetWidth

scrollTop

)

SHOULD batch DOM reads/writes (avoid interleaving)
SHOULD prefer uncontrolled inputs; controlled inputs must be cheap per keystroke
SHOULD add
```
<link rel="preconnect">
```
for CDN/asset domains

SHOULD preload critical fonts (

<link rel="preload" as="font">

) and use

font-display: swap

Design

NEVER use gradients unless explicitly requested
NEVER use purple or multicolor gradients
NEVER use glow effects as primary affordances
SHOULD use Tailwind CSS default shadow scale unless explicitly requested
MUST give empty states one clear next action
SHOULD limit accent color usage to one per view
SHOULD use existing theme or Tailwind CSS color tokens before introducing new ones

Design Direction (when aesthetics requested)

MUST choose a clear aesthetic direction and execute consistently (e.g., brutally minimal, editorial, utilitarian, playful)
SHOULD use deliberate typography (1 display + 1 body) and avoid accidental defaults; follow product font system when it exists
SHOULD define theme/palette via CSS variables; use one dominant base + sharp accent
SHOULD match implementation complexity to the aesthetic (minimal = restraint; maximal = elaborate but controlled)
If motion is explicitly requested: prefer one cohesive high-impact sequence (load stagger, scroll reveal) over scattered micro-interactions
SHOULD avoid cookie-cutter layout/component patterns; make 1-2 distinctive choices grounded in context

Content & Copy

SHOULD use active voice ("Install the CLI" not "The CLI will be installed")
SHOULD use specific button labels ("Save API Key" not "Continue")
SHOULD write error messages with a fix/next step, not just the problem
SHOULD write in second person; avoid first person
SHOULD use
```
&
```
over "and" where space-constrained

Anti-patterns (flag these)

```
user-scalable=no
```
or
```
maximum-scale=1
```
disabling zoom
```
onPaste
```
with
```
preventDefault
```
```
transition: all
```
```
outline-none
```
without a
```
focus-visible
```
replacement
Inline
```
onClick
```
navigation without
```
<a>
```
/
```
<Link>
```
```
<div>
```
/
```
<span>
```
with click handlers (use
```
<button>
```
)
Images without dimensions
Large arrays
```
.map()
```
without virtualization
Form inputs without labels
Icon buttons without
```
aria-label
```
Hardcoded date/number formats (use
```
Intl.*
```
)
```
autoFocus
```
without clear justification

Rules if not found in primitives

The below rules apply if the pattern is either explicitly requested or not found in the primitive itself already.

Accessibility

Icon-only buttons need
```
aria-label
```
Form controls need
```
<label>
```
or
```
aria-label
```
Interactive elements need keyboard handlers (
```
onKeyDown
```
/
```
onKeyUp
```
)
```
<button>
```
for actions,
```
<a>
```
/
```
<Link>
```
for navigation (not
```
<div onClick>
```
)
Images need
```
alt
```
(or
```
alt=""
```
if decorative)
Decorative icons need
```
aria-hidden="true"
```
Async updates (toasts, validation) need
```
aria-live="polite"
```
Use semantic HTML (
```
<button>
```
,
```
<a>
```
,
```
<label>
```
,
```
<table>
```
) before ARIA
Headings hierarchical
```
<h1>
```
–
```
<h6>
```
; include skip link for main content
```
scroll-margin-top
```
on heading anchors

Focus States

Interactive elements need visible focus:
```
focus-visible:ring-*
```
or equivalent
Never
```
outline-none
```
/
```
outline: none
```
without focus replacement
Use
```
:focus-visible
```
over
```
:focus
```
(avoid focus ring on click)
Group focus with
```
:focus-within
```
for compound controls

Forms

Inputs need
```
autocomplete
```
and meaningful
```
name
```
Use correct
```
type
```
(
```
email
```
,
```
tel
```
,
```
url
```
,
```
number
```
) and
```
inputmode
```
Never block paste (
```
onPaste
```
+
```
preventDefault
```
)
Labels clickable (
```
htmlFor
```
or wrapping control)
Disable spellcheck on emails, codes, usernames (
```
spellCheck={false}
```
)
Checkboxes/radios: label + control share single hit target (no dead zones)
Submit button stays enabled until request starts; spinner during request
Errors inline next to fields; focus first error on submit
Placeholders end with
```
…
```
and show example pattern
```
autocomplete="off"
```
on non-auth fields to avoid password manager triggers
Warn before navigation with unsaved changes (
```
beforeunload
```
or router guard)

web-ui-best-practices

NPX Install

Tags

SKILL.md Content