Thirty-three isometric line figures that answer the pointer. For React and for anything with a DOM.

Live, with a slider for intensity: hairline.lucasmarkes.com

npm i @lucasmarkes/hairline

No dependencies. ESM only. React 18 or later is an optional peer, needed only by @lucasmarkes/hairline/react.

With shadcn, which adds the package and a wrapper that reads your theme's tokens:

npx shadcn@latest add https://hairline.lucasmarkes.com/r/hairline.json

import { Terrain } from "@lucasmarkes/hairline/react";

export function Hero() {
  return <Terrain />;
}

The figure fills its parent's width at a 5:4 aspect ratio. The entry is a client module, so a Server Component can render it with no "use client" of its own. Every component takes the options below and every <div> attribute, and forwards its ref to the <div>.

import { terrain } from "@lucasmarkes/hairline";

const figure = terrain(document.getElementById("figure")!, { play: true });

figure.update({ intensity: 0.8 });
figure.destroy();

A figure draws into the element you give it, at the element's width and a 5:4 aspect ratio. update changes options on the running figure; destroy removes what the figure added. That is the shape of a Svelte action, so use:terrain={{ intensity }} works as it is.

Every figure takes the same five, all optional:

In update, a key set to undefined goes back to its default, and a key left out stays as it is.

Six custom properties, set on the figure or on anything above it:

.figures {
  --hairline-plate: #101014; /* the fill of every plate: the colour the figure sits on */
  --hairline-hi: #fafafa;    /* what is lit */
  --hairline-edge: #a1a1aa;  /* silhouettes */
  --hairline-mid: #52525b;   /* every other stroke */
  --hairline-lo: #27272a;    /* what recedes */
  --hairline-stroke: 0.9;    /* stroke width, in CSS pixels at any size */
}

--hairline-plate is the one to get right. Plates are filled, not transparent, because a plate hides what is drawn behind it; on a background that is neither white nor #08090a, set it to that background.

The figure's styles have no specificity, so any rule of yours wins without !important.

• Accessibility. A figure is an image with a description you can replace with label. Riffle is the exception: it is a focusable group, the arrow keys walk its cards, and a live region reads the card out.
• Reduced motion. With prefers-reduced-motion, the figures that play on their own (Phosphor and Slow) hold still, a figure given play rests, and every figure still answers the pointer.
• Performance. Every figure on a page shares one requestAnimationFrame loop. A figure off screen, or at rest, does no work, and the loop stops when nothing is moving; a figure given play keeps it running while it is on screen.
• Server rendering. On the server a component is an empty box with a 5:4 aspect ratio, so nothing shifts when it draws. The functions need a DOM: call them in an effect, in onMount, or in a script after the element.
• Shadow DOM. A figure mounted inside a shadow root styles itself there.

hairline-create is a skill for coding agents. Give it an idea and it draws a new figure to Hairline's ten rules, on the same engine as the thirty-three above, as one HTML file. Every figure it makes declares a tour, the stops a hand would visit, and the page it writes has a play button that walks it.

npx skills add lucasmarkes/hairline

Then type the command with an idea in the agent:

/hairline-create a sales funnel

It offers two or three concepts, draws the one you pick, checks it against the rules and in a browser, and hands over hairline-<name>.html: one file with no dependencies that opens from disk. It runs on any agent that reads skills: Claude Code, Cursor, Codex and others.

With a drawing you already have, an icon or a logo as an SVG, hairline-adopt reads it, rebuilds its object as a figure with its proportions and its parts, and proposes what the pointer does to it:

/hairline-adopt icons/deploy.svg

What both skills drew, each beside its prompt: hairline.lucasmarkes.com/skills.

• hairline.lucasmarkes.com: every figure live, an inspector that writes the snippet for you, and a CDN example.
• How Hairline was made: the brief, the arguing, and every correction written down as a rule.
• The essay: how the figures are drawn, and why with lines.
• CHANGELOG.md and CONTRIBUTING.md.

MIT © Lucas Marques