# DESIGN.md: Anthropic-style design system

Measured from https://www.anthropic.com/ on 2026-10-14 by PikSpec (https://www.pikspec.com). An independent measurement of the rendered page, not Anthropic's official design system, and not affiliated with Anthropic.

Use it to build your own product in this design language: put this file in your project root and tell your AI tool (Claude Code, Cursor, Codex, Lovable, v0) to follow DESIGN.md. Never use the original's name, logo, copy or images; licensed fonts are replaced with the closest free Google Fonts.

To capture any other page, or get a ready project for your tool: https://www.pikspec.com/build-with-ai

HOW IT SHOULD LOOK
Build it in the design language of anthropic.com, measured from the live site: it should feel designed by the same team as anthropic.com — the same temperament, colour, type and density — for a different product. Never use anthropic.com's name, logo, words or images.

Stack: use the one your project already has. Starting fresh: React + Vite + TypeScript + Tailwind CSS v4, with no UI kit (no shadcn/ui, MUI or Chakra) — their defaults would override this system. In a chat that shows one file (an artifact or canvas), build one HTML file instead, with the tokens below in its <style> block.
Use every value exactly as written. Do not round, rename, approximate or substitute a colour, size, radius, shadow or easing (fonts: see section 1). Anything not listed here does not exist in this system.

THE WEBSITE THIS SYSTEM COMES FROM
- Reference page: https://www.anthropic.com/ — "www.anthropic.com" (home page).
- Page frame: a top navigation bar and a footer.
- Content is grouped in cards (8 on the page). Keep cards for grouped content only, not for every section.
- It uses 4 images. Images are supporting, not the hero — keep them small and purposeful.
- Interaction: 8 buttons on one page.
- The page runs about 4 screens long at 1440px wide.
- Density is moderate.

HOW IT LOOKS (WHAT MAKES IT LOOK LIKE ITSELF, BEYOND THE VALUES)
- Almost entirely neutral: 100% of the page is painted in #F0EEE6 and #141413.
- The largest type (60.87px Anthropic Sans) is bold (700).
- Balanced: text covers 14% of the page.
- Share of the painted page: #F0EEE6 48% (dominant, backgrounds); #141413 28% (dominant, backgrounds and text); #FAF9F5 14.3% (supporting, backgrounds); #E3DACC 8.1% (supporting, backgrounds); #B0AEA5 1.5% (supporting, text). Keep accents at these proportions; do not promote them to fills.
- Hairline dividers: 1px lines in #141413 separate sections and rows (26 of them).
- Small marks: 4 small decorative marks (dots, crosses or ticks under 16px) in #FAF9F5, placed at corners and edges.
- Type as set (size, weight and tracking measured together; use these pairs): 60.87px weight 700; 24px weight 600; 22.4px weight 400; 20px weight 400; 18px weight 400; 16px weight 600.

1. DESIGN TOKENS — PASTE INTO YOUR GLOBAL CSS
Allowed colours, with how the original uses each. Use no other colour, including in hover states:
- #F0EEE6 — 48% · backgrounds (var(--color-background))
- #141413 — 28% · backgrounds, text (var(--color-text))
- #FAF9F5 — 14.3% · backgrounds (var(--color-surface))
- #E3DACC — 8.1% · backgrounds (var(--color-e3dacc))
- #B0AEA5 — 1.5% · text
- #D97757 — Negative (var(--color-negative))
- #C6613F — Warning (var(--color-warning))
Fonts — put these first in your global CSS (one import per font, so one that fails cannot stop the others):
```css
@import url("https://fonts.googleapis.com/css2?family=Figtree:wght@400;500;600;700&display=swap");
@import url("https://fonts.googleapis.com/css2?family=Source+Serif+4:wght@400;500;600&display=swap");
@import url("https://fonts.googleapis.com/css2?family=JetBrains+Mono:wght@400&display=swap");
```
Font: anthropic.com uses Anthropic Sans (body), Anthropic Serif (display) and Anthropic Mono (code) — its own licensed faces, not available to download. This kit uses Figtree for body, Source Serif 4 for display and JetBrains Mono for code, the closest free matches, already in the tokens. If you own the original, add it with @font-face and it is used first; to use another font, change the --font-* variables.
Keep every size, weight, line height and tracking exactly as listed whichever font renders.
```css
:root {
  --color-background: #F0EEE6; /* Background */
  --color-surface: #FAF9F5; /* Surface */
  --color-text: #141413; /* Text */
  --color-negative: #D97757; /* Negative */
  --color-warning: #C6613F; /* Warning */
  --color-e3dacc: #E3DACC; /* 8.1% of the page, as fills */
  --font-body: "Anthropic Sans", "Figtree", sans-serif; /* Anthropic Sans on the site; Figtree renders */
  --font-display: "Anthropic Serif", "Source Serif 4", serif; /* Anthropic Serif on the site; Source Serif 4 renders */
  --font-code: "Anthropic Mono", "JetBrains Mono", monospace; /* Anthropic Mono on the site; JetBrains Mono renders */
  --type-display: 60.87px; /* Display, weight 700 */
  --type-display-leading: 66.9518px;
  --type-headline: 24px; /* Headline, weight 600 */
  --type-headline-leading: 31.2px;
  --type-title-large: 22.4px; /* Title Large, weight 400 */
  --type-title-large-leading: 31.36px;
  --type-title-medium: 20px; /* Title Medium, weight 400 */
  --type-title-medium-leading: 28px;
  --type-title-small: 18px; /* Title Small, weight 400 */
  --type-title-small-leading: 25.2px;
  --type-body-large: 16px; /* Body Large, weight 600 */
  --type-body-large-leading: 22.4px;
  --type-body-small: 15px; /* Body Small, weight 400 */
  --type-body-small-leading: 15px;
  --type-body-small-tracking: -0.005em;
  --type-label: 12px; /* Label, weight 400 */
  --type-label-leading: 16.8px;
  --type-label-tracking: -0.02em;
  --space-4: 4px;
  --space-8: 8px;
  --space-12: 12px;
  --space-16: 16px;
  --space-24: 24px;
  --space-28: 28px;
  --space-32: 32px;
  --space-76: 76px;
  --space-100: 100px;
  --radius-md: 6px;
  --radius-lg: 8px;
  --radius-xl: 12px;
  --radius-2xl: 16px;
  --radius-3xl: 24px;
  --radius-full: 9999px;
  --duration-1: 0.06s;
  --duration-2: 0.2s;
  --duration-3: 0.3s;
  --duration-4: 0.45s;
  --ease-1: cubic-bezier(0.2, 0.8, 0.2, 1);
  --ease-2: ease-out;
}
```
Tailwind CSS v4 (the default for new projects): put this after `@import "tailwindcss";`. It removes Tailwind's own palette, so only these colours exist as utilities:
```css
@theme {
  --color-*: initial;
  --color-background: #F0EEE6;
  --color-surface: #FAF9F5;
  --color-text: #141413;
  --color-negative: #D97757;
  --color-warning: #C6613F;
  --color-e3dacc: #E3DACC;
  --font-body: "Anthropic Sans", "Figtree", sans-serif;
  --font-display: "Anthropic Serif", "Source Serif 4", serif;
  --font-code: "Anthropic Mono", "JetBrains Mono", monospace;
  --text-display: 60.87px;
  --text-display--line-height: 66.9518px;
  --text-headline: 24px;
  --text-headline--line-height: 31.2px;
  --text-title-large: 22.4px;
  --text-title-large--line-height: 31.36px;
  --text-title-medium: 20px;
  --text-title-medium--line-height: 28px;
  --text-title-small: 18px;
  --text-title-small--line-height: 25.2px;
  --text-body-large: 16px;
  --text-body-large--line-height: 22.4px;
  --text-body-small: 15px;
  --text-body-small--line-height: 15px;
  --text-body-small--letter-spacing: -0.005em;
  --text-label: 12px;
  --text-label--line-height: 16.8px;
  --text-label--letter-spacing: -0.02em;
  --radius-md: 6px;
  --radius-lg: 8px;
  --radius-xl: 12px;
  --radius-2xl: 16px;
  --radius-3xl: 24px;
  --radius-full: 9999px;
  --ease-1: cubic-bezier(0.2, 0.8, 0.2, 1);
  --ease-2: ease-out;
}
```
Tailwind CSS v3 only: extend the theme with these instead, and use no other palette:
```js
// tailwind.config — theme.extend
{
  colors: { "background": "var(--color-background)", "surface": "var(--color-surface)", "text": "var(--color-text)", "negative": "var(--color-negative)", "warning": "var(--color-warning)" },
  fontFamily: { "body": ["var(--font-body)"], "display": ["var(--font-display)"], "code": ["var(--font-code)"] },
  borderRadius: { "md": "var(--radius-md)", "lg": "var(--radius-lg)", "xl": "var(--radius-xl)", "2xl": "var(--radius-2xl)", "3xl": "var(--radius-3xl)", "full": "var(--radius-full)" },
}
```

2. BASE STYLES
```css
html { background: var(--color-background); }
body { margin: 0; font-family: var(--font-body); font-size: var(--type-body-large); line-height: var(--type-body-large-leading); color: var(--color-text); -webkit-font-smoothing: antialiased; -moz-osx-font-smoothing: grayscale; }
h1, h2, h3 { font-family: var(--font-display); margin: 0; }
a { color: inherit; }
:focus-visible { outline: 2px solid var(--color-text); outline-offset: 2px; }
```

3. COMPONENTS — MATCH THESE EXACTLY
```css
.link-2 { /* Inline 2 */
  background: transparent;
  min-height: 54px;
  color: var(--color-text);
  font-family: var(--font-body);
  font-size: var(--type-body-large);
  font-weight: 500;
  line-height: 22.4px;
  /* recorded states: active, hover, focus-visible */
}
.link-3 { /* Inline 3 */
  background: transparent;
  color: #B0AEA5;
  font-family: var(--font-body);
  font-size: var(--type-label);
  font-weight: 400;
  line-height: 16.8px;
  /* recorded states: active, hover, focus-visible */
}
.card { /* Default */
  background: var(--color-surface);
  border-radius: var(--radius-md);
  color: var(--color-text);
  font-family: var(--font-display);
  font-size: var(--type-title-medium);
  font-weight: 400;
  line-height: 28px;
}
.nav { /* Default */
  background: transparent;
  min-height: 68px;
  color: var(--color-text);
  font-family: var(--font-display);
  font-size: var(--type-title-medium);
  font-weight: 400;
  line-height: 28px;
}
.button { /* Tertiary */
  background: transparent;
  padding: 22px 12px 22px 12px;
  min-height: 69px;
  color: var(--color-text);
  font-family: var(--font-display);
  font-size: var(--type-title-medium);
  font-weight: 400;
  line-height: 28px;
  /* recorded states: collapsed, focus, hover, focus-visible */
}
.button-2 { /* Tertiary 2 */
  background: transparent;
  color: #B0AEA5;
  font-family: var(--font-body);
  font-size: var(--type-label);
  font-weight: 400;
  line-height: 16.8px;
  /* recorded states: hover, focus-visible */
}
```
Where a component lists recorded states, write those states using only the colours above; the capture saw that the state exists, not its values. Never invent a state colour.

4. PAGE COMPOSITION
- Light interface on #F0EEE6. Keep that ground; do not add a dark mode or alternate section backgrounds the system does not have.
- Type: Figtree (standing in for Anthropic Sans) for body; Source Serif 4 (standing in for Anthropic Serif) for display; JetBrains Mono (standing in for Anthropic Mono) for code. Hierarchy comes from size and weight, not colour or decoration.
- Corner radii are 6px, 8px, 12px, 16px, 24px, fully round (pill) — nothing else.
- The system is flat: no drop shadows.
- Body text uses Anthropic Sans at around 16px, weights 400, 500, 600, 700.
- Headings use Anthropic Serif; the largest heading is 79.72px.
- Cards use 8px 0px 0px 8px corners.
- Corner radii in use: 8px, 24px, 12px, 9999px (pill), 6px.

HOW THE ORIGINAL PACES ITS PAGE (BORROW THE RHYTHM — THE OPENING, THE COLOURED BANDS, THE CARD GRIDS — NOT THE LIST; BUILD THE SECTIONS YOUR PRODUCT NEEDS)
1. Hero — 390px tall, split 7 / 5, 31px gap, centred 60.87px heading (weight 700).
2. Grid — 726px tall, 4 items in 3 columns with 173px gaps, centred 22.4px heading (weight 400) set low in the band, image centred, on #FAF9F5.
3. Cards — 617px tall, 3 equal columns, 31px gap, left-aligned 24px heading (weight 600).
4. Split — 514px tall, split 4 / 8, 31px gap, left-aligned 24px heading (weight 600).
5. Footer — 1009px tall, split 3 / 9, 31px gap, centred 12px heading (weight 400), on #141413.
- Content sits in a 1285px container, 78px from the edge at 1440px wide.
- A 68px header scrolls away.
- The hero is 390px (0.4 screens): split 7 / 5, 31px gap, centred 60.87px heading (weight 700).
- Column splits on a 12-column grid: thirds (2×), 7/5, 4/8, 3/9; gaps of 31px.
- Headings mix left (2) and centred (3) alignment.
- Sections change background 3 times, between #FAF9F5, #141413: colour comes in full-width bands, not in boxes.
- A typical section is about 617px tall.

COPY SHAPE (MATCH THE LENGTH AND CASE; WRITE YOUR OWN WORDS)
- The main heading is 19 words long.
- Section headings are short: typically 2 words.
- Heading case varies.
- The page describes itself in about 18 words; keep your intro paragraph to about that length.

5. MOTION
Interactive elements change colour, background, border and opacity with the measured timing. Animate nothing else.
```css
a, button, [role="button"], input { transition: color var(--duration-1) var(--ease-1), background-color var(--duration-1) var(--ease-1), border-color var(--duration-1) var(--ease-1), opacity var(--duration-1) var(--ease-1); }
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation-duration: 0.01ms !important; animation-iteration-count: 1 !important; transition-duration: 0.01ms !important; scroll-behavior: auto !important; }
}
```
No scroll-triggered fade-ins, parallax, typewriter text or bouncing elements.

6. RESPONSIVE
- The design was measured at 1440px wide. Lay it out for that width first, then let it reflow down to 360px.
- Content sits in a column at most 1285px wide, centred, with var(--space-16) (16px) side padding on small screens.
- The largest heading scales fluidly: font-size: clamp(24px, 4.2vw, 60.87px). Every other size stays fixed.
- Break on composition, not device names: a row of columns drops a column when any column would be narrower than 240px; side-by-side splits stack when either side would be narrower than 320px.
- Spacing steps never change between sizes; use smaller steps from the same list where space is tight.
- On touch screens, every link and button has a hit area of at least 44 × 44px without changing its drawn size.

7. ACCESSIBILITY
- Text pairs that pass for body copy: Text on Background (15.9:1) and Text on Surface (17.5:1).
- Only for text 24px and up, or 18.66px bold: Negative on Surface (3:1).
- Use no other text-on-background pairing.
- One h1 per page, headings in order, landmarks (header, nav, main, footer), real buttons and links, a label on every field, alt text on every image, an aria-label on icon-only buttons.
- Every interactive element shows the :focus-visible outline above.

8. DO NOT (THESE ARE WHAT MAKE AI-BUILT SITES LOOK GENERIC)
- No drop shadows anywhere, including cards, buttons and images. (No box-shadow was measured on the page.)
- No gradients: not in backgrounds, text, buttons or borders. (No gradient was measured.)
- Only these colours: #F0EEE6, #141413, #FAF9F5, #E3DACC, #B0AEA5, #D97757, #C6613F. No new tints, no Tailwind defaults (slate, indigo, violet). (They are every colour that covers a measurable part of the page, and the colours its lines and drawings use.)
- Only the fonts in the tokens: Figtree for body; Source Serif 4 for display; JetBrains Mono for code. No other typeface, and no Inter, Roboto or system UI font unless it is one of these. (The page is set in Anthropic Sans and Anthropic Serif and Anthropic Mono; the tokens carry what stands in for them.)
- Headings and large text never heavier than weight 700. Do not make headlines bold to add emphasis. (Every size from 24px up is set at weight 700 or lighter.)
- No stock photography or AI-generated photos. (Photographs cover almost none of the page.)
- No icon above every feature, no emoji, no decorative blobs, sparkles or glows. (None of these is part of the captured design; they are a coding model's defaults.)
- Build the sections your product needs, not the original's list. Give each one this system's look: its kinds of section (hero, grid, cards, split, footer), its colours, type, shapes and spacing. (The style carries to any kind of site; the original's page was for a different product.)
- No glassmorphism, backdrop blur, glowing orbs, noise blobs or neon outlines.
- No row of three identical feature cards as the default section. Vary the layout from section to section: a split, a list, a single large statement, a table.
- No centred-everything hero with a pill badge, a gradient headline and two buttons. Lead with the most specific thing about the product.
- No filler copy: no "Unlock your potential", "Revolutionize", "Seamless", "Elevate", "Supercharge", "Next-gen" or lorem ipsum. Write plain, specific sentences a real company would publish.
- No made-up statistics, testimonials or customer logos. Leave a clearly marked [content: …] slot instead.
- No radius larger than the largest one listed.
- Do not use anthropic.com's name, logo, copy or images. This is its design system, not its content.

BEFORE YOU FINISH
- Search your code for every colour, font size, spacing value, radius, shadow and easing, and replace anything that is not a variable above.
- Check that no [content: …] slot has been filled with invented facts.
- Search your CSS for box-shadow and filter: drop-shadow. There should be none.
- Search your CSS for gradient(. There should be none.
- Every colour value in your CSS is one of the allowed colours. Nothing else, including in hover states.
- No text 24px or larger has a font-weight above 700.
- Every section, including ones the original does not have, uses only this system's colours, type, shapes and spacing.
- Content sits in a 1285px container with 78px side margins at 1440px.
- There is no placeholder copy (lorem ipsum, "Feature one", "Your headline here"). Every word is real.
- Take a screenshot at 1440px and put it beside the original. List every difference in colour, weight, spacing, alignment and imagery, and fix each before finishing. Then check 390px wide: nothing scrolls sideways and no heading runs off the screen.