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