Generative UI

Generative UI Skill

This skill contains the complete design system for Claude's built-in show_widget tool — the generative UI feature that renders interactive HTML/SVG widgets inline in claude.ai conversations. The guidelines below are the actual Anthropic "Imagine — Visual Creation Suite" design rules, extracted so you can produce high-quality widgets directly without needing the read_me setup call.

How it works: On claude.ai, Claude has access to the show_widget tool which renders raw HTML/SVG fragments inline in the conversation. This skill provides the design system, templates, and patterns to use it well.

Step 1: Pick the Right Visual Type

Route on the verb, not the noun. Same subject, different visual depending on what was asked:

Step 2: Build the Widget

Structure (strict order)

<style>  →  HTML content  →  <script>

Output streams token-by-token. Styles must exist before the elements they target, and scripts must run after the DOM is ready.

Philosophy

• Seamless: Users shouldn't notice where the host UI ends and your widget begins
• Flat: No gradients, mesh backgrounds, noise textures, or decorative effects. Clean flat surfaces
• Compact: Show the essential inline. Explain the rest in text
• Text goes in your response, visuals go in the tool — all explanatory text, descriptions, and summaries must be written as normal response text OUTSIDE the tool call. The tool output should contain ONLY the visual element

Core Rules

• No <!-- comments --> or /* comments */ (waste tokens, break streaming)
• No font-size below 11px
• No emoji — use CSS shapes or SVG paths
• No gradients, drop shadows, blur, glow, or neon effects
• No dark/colored backgrounds on outer containers (transparent only — host provides the bg)
• Typography: two weights only: 400 regular, 500 medium. Never use 600 or 700. Headings: h1=22px, h2=18px, h3=16px — all font-weight 500. Body text=16px, weight 400, line-height 1.7
• Sentence case always. Never Title Case, never ALL CAPS
• No mid-sentence bolding — entity names go in code style not bold
• No <!DOCTYPE>, <html>, <head>, or <body> — just content fragments
• No position: fixed — use normal-flow layouts
• No tabs, carousels, or display: none sections during streaming
• No nested scrolling — auto-fit height
• Corners: border-radius: var(--border-radius-lg) for cards, var(--border-radius-md) for elements
• No rounded corners on single-sided borders (border-left, border-top)
• Round every displayed number — use Math.round(), .toFixed(n), or Intl.NumberFormat

CDN Allowlist (CSP-enforced)

External resources may ONLY load from:

• cdnjs.cloudflare.com
• cdn.jsdelivr.net
• unpkg.com
• esm.sh

All other origins are blocked — the request silently fails.

CSS Variables

Backgrounds: --color-background-primary (white), -secondary (surfaces), -tertiary (page bg), -info, -danger, -success, -warning Text: --color-text-primary (black), -secondary (muted), -tertiary (hints), -info, -danger, -success, -warning Borders: --color-border-tertiary (0.15α, default), -secondary (0.3α, hover), -primary (0.4α), semantic -info/-danger/-success/-warning Typography: --font-sans, --font-serif, --font-mono Layout: --border-radius-md (8px), --border-radius-lg (12px), --border-radius-xl (16px)

All auto-adapt to light/dark mode.

Dark mode is mandatory — every color must work in both modes:

• In HTML: always use CSS variables for text. Never hardcode colors like color: #333
• In SVG: use pre-built color classes (c-blue, c-teal, etc.) — they handle light/dark automatically
• Mental test: if the background were near-black, would every text element still be readable?

sendPrompt(text)

A global function that sends a message to chat as if the user typed it. Use it when the user's next step benefits from Claude thinking. Handle filtering, sorting, toggling, and calculations in JS instead.

Step 3: Render with show_widget

The show_widget tool is built into claude.ai — no activation needed. Pass your widget code directly:

{
  "title": "snake_case_widget_name",
  "widget_code": "<style>...</style>\n<div>...</div>\n<script>...</script>"
}

For SVG output: start widget_code with <svg — it will be auto-detected and wrapped appropriately.

Step 4: Chart.js Template

For charts, use onload callback pattern to handle script load ordering:

<div style="display: grid; grid-template-columns: repeat(auto-fit, minmax(140px, 1fr)); gap: 12px;">
  <div style="background: var(--color-background-secondary); border-radius: var(--border-radius-md); padding: 1rem;">
    <div style="font-size: 13px; color: var(--color-text-secondary);">Label</div>
    <div style="font-size: 24px; font-weight: 500;" id="stat1">—</div>
  </div>
</div>

<div style="position: relative; width: 100%; height: 300px; margin-top: 1rem;">
  <canvas id="myChart"></canvas>
</div>

<div style="display: flex; align-items: center; gap: 12px; margin-top: 1rem;">
  <label style="font-size: 14px; color: var(--color-text-secondary);">Parameter</label>
  <input type="range" min="0" max="100" value="50" id="param" step="1" style="flex: 1;" />
  <span style="font-size: 14px; font-weight: 500; min-width: 32px;" id="param-out">50</span>
</div>

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/4.5.1/chart.umd.js" onload="initChart()"></script>
<script>
function initChart() {
  const slider = document.getElementById('param');
  const out = document.getElementById('param-out');
  let chart = null;

  function update() {
    const val = parseFloat(slider.value);
    out.textContent = val;
    document.getElementById('stat1').textContent = val.toFixed(1);

    const labels = [], data = [];
    for (let x = 0; x <= 100; x++) {
      labels.push(x);
      data.push(x * val / 100);
    }

    if (chart) chart.destroy();
    chart = new Chart(document.getElementById('myChart'), {
      type: 'line',
      data: { labels, datasets: [{ data, borderColor: '#7F77DD', borderWidth: 2, pointRadius: 0, fill: false }] },
      options: {
        responsive: true,
        maintainAspectRatio: false,
        plugins: { legend: { display: false } },
        scales: { x: { grid: { display: false } } }
      }
    });
  }

  slider.addEventListener('input', update);
  update();
}
if (window.Chart) initChart();
</script>

Chart.js rules:

• Canvas cannot resolve CSS variables — use hardcoded hex
• Set height ONLY on the wrapper div, never on canvas itself
• Always responsive: true, maintainAspectRatio: false
• Always disable default legend, build custom HTML legends
• Number formatting: -$5M not $-5M (negative sign before currency symbol)
• Use onload="initChart()" on CDN script tag + if (window.Chart) initChart(); as fallback

Step 5: SVG Diagram Template

For flowcharts and diagrams, use SVG with pre-built classes:

<svg width="100%" viewBox="0 0 680 H">
  <defs>
    <marker id="arrow" viewBox="0 0 10 10" refX="8" refY="5" markerWidth="6" markerHeight="6" orient="auto-start-reverse">