anthropic-ui-skills

Anthropic UI Skills

Opinionated constraints for building Anthropic-style interfaces with AI agents.

When to Apply

Reference these guidelines when:

• Building light-mode interfaces
• Creating Anthropic-inspired design systems
• Implementing UIs with Inter font and 4px grid

Colors

• SHOULD use light backgrounds for primary surfaces
• MUST use #ECE9E0 as page background (surface-base)
• SHOULD limit color palette to 8 distinct colors
• MUST maintain text contrast ratio of at least 4.5:1 for accessibility

Semantic Tokens

Token	HEX	RGB	Usage
surface-base	#ECE9E0	rgb(236,233,224)	Page background
surface-raised	#DBD1C0	rgb(219,209,192)	Cards, modals, raised surfaces
surface-overlay	#0F0F10	rgb(15,15,16)	Overlays, tooltips, dropdowns
text-primary	#625F59	rgb(98,95,89)	Headings, body text
text-secondary	#9F9F9C	rgb(159,159,156)	Secondary, muted text
text-tertiary	#454036	rgb(69,64,54)	Additional text

Typography

• MUST use Inter as primary font family
• SHOULD use single font family for consistency
• MUST use 68px / 700 for primary headings
• MUST use 33px / semi_bold for body text
• SHOULD reduce font weights (currently 5 detected)
• MUST use text-balance for headings and text-pretty for body text
• SHOULD use tabular-nums for numeric data
• NEVER modify letter-spacing unless explicitly requested

Text Styles

Style	Font	Size	Weight	Color	Count
heading-1	Inter	68px	700	#201F1D	1
body	Inter	33px	semi_bold	#35312A	1
text-23px	Inter	23px	500	#403D37	1
text-21px	Inter	21px	400	#3D362C	1
text-21px	Inter	21px	400	#3B352B	1
text-20px	Inter	20px	400	#494237	1
text-17px	Inter	17px	500	#423F3B	1
text-16px	Inter	16px	400	#454036	1
text-14px	Inter	14px	500	#3F3931	1
text-14px	Inter	14px	400	#A2A3A0	1

Typography Reference

Font Families:

• Inter (used 16x)

Font Sizes: 10px, 11px, 14px, 16px, 17px, 20px, 21px, 23px, 33px, 68px

Spacing

• MUST use 4px grid for spacing
• SHOULD use spacing from scale: 3px, 4px, 5px, 6px
• SHOULD use 5px as default gap between elements
• NEVER use arbitrary spacing values (use design scale)
• SHOULD maintain consistent padding within containers

Borders

• MUST use border-radius from scale: 3px, 15px
• SHOULD use 3px as default border-radius
• NEVER use arbitrary border-radius values (use design scale)
• SHOULD use subtle borders (1px) for element separation

Border Radius Reference

Scale: 3px, 15px

Layout

• MUST design for 1920px base viewport width
• SHOULD use consistent element widths: 10px, 18px, 146px, 579px
• SHOULD maintain text-heavy layout with clear hierarchy
• NEVER use h-screen, use h-dvh for full viewport height
• MUST respect safe-area-inset for fixed elements
• SHOULD use size-* for square elements instead of w-* + h-*

Detected Layout Patterns

• Main Content: width: 1920px, height: 1004px
• Main Content: width: 1920px, height: 673px

Components

• MUST use 0px height for input fields

Buttons

Variant	Background	Text	Border	Height	Radius
Ghost	transparent	#9F9F9C	none	-	-

Inputs

• Height: 0px

Interactive States

Focus

• MUST use 2px outline with accent color (#5E6AD2)
• MUST use 2px outline-offset
• NEVER remove focus indicators

Hover

• Buttons (primary): lighten background by 10%
• Buttons (secondary): use #DBD1C0 background
• List items: use #DBD1C0 background

Disabled

• MUST use opacity: 0.5
• MUST use cursor: not-allowed

Interaction

• MUST use an AlertDialog for destructive or irreversible actions
• SHOULD use structural skeletons for loading states
• MUST show errors next to where the action happens
• NEVER block paste in input or textarea elements
• MUST add an aria-label to icon-only buttons

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 use ease-out on entrance animations
• NEVER exceed 200ms for interaction feedback
• SHOULD respect prefers-reduced-motion

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