Generative UI skill

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.

Codex and other hosts: First check the available tools. Use the host's documented visualization interface when provided; otherwise save a complete HTML document in the workspace and return a clickable file link. For standalone output, the fragment-only rule below does not apply: include a document wrapper and viewport metadata, define the CSS variables and SVG classes used by the templates (including dark-mode colors), and load chart dependencies explicitly. The host-specific CDN allowlist and injected styles below describe Claude's renderer; they are not Codex capabilities. Remove chat follow-up buttons and sendPrompt handlers when that bridge is unavailable; keep local sliders and calculations functional. Verify the saved output in a browser when available.

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Step 1: Pick the Right Visual Type

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

User says	Type	Format
"how does X work"	Illustrative diagram	SVG
"X architecture"	Structural diagram	SVG
"what are the steps"	Flowchart	SVG
"explain compound interest"	Interactive explainer	HTML
"compare these options"	Comparison grid	HTML
"show revenue chart"	Chart.js chart	HTML
"create a contact card"	Data record	HTML
"draw a sunset"	Art/illustration	SVG

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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
• No stock "AI design" defaults: skip cream or off-white panels, italic accent words in headings, numbered "01 / 02 / 03" section labels, monospace labels outside code, and pill-shaped buttons — they read as generic and clash with the host UI
• Text goes in your response, visuals go in the tool — write explanatory text, descriptions, and summaries as normal response text outside the tool call; the widget holds 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.

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Step 3: Render with the Available Host

When the host exposes show_widget, pass your widget code directly as below. In Codex without that tool, follow the standalone HTML path above; do not invent a show_widget call.

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

Parameter	Type	Required	Description
title	string	Yes	Snake_case identifier for the widget
widget_code	string	Yes	HTML or SVG code. For SVG: start with <svg>. For HTML: content fragment

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">
      <path d="M2 1L8 5L2 9" fill="none" stroke="context-stroke" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
    </marker>
  </defs>

  <!-- Single-line node (44px tall) -->
  <g class="node c-blue" onclick="sendPrompt('Tell me more about this')">
    <rect x="250" y="40" width="180" height="44" rx="8" stroke-width="0.5"/>
    <text class="th" x="340" y="62" text-anchor="middle" dominant-baseline="central">Step one</text>
  </g>

  <!-- Connector arrow -->
  <line x1="340" y1="84" x2="340" y2="120" class="arr" marker-end="url(#arrow)"/>

  <!-- Two-line node (56px tall) -->
  <g class="node c-teal" onclick="sendPrompt('Explain this step')">
    <rect x="230" y="120" width="220" height="56" rx="8" stroke-width="0.5"/>
    <text class="th" x="340" y="140" text-anchor="middle" dominant-baseline="central">Step two</text>
    <text class="ts" x="340" y="158" text-anchor="middle" dominant-baseline="central">Processes the input</text>
  </g>
</svg>

SVG rules:

• ViewBox always 680px wide (viewBox="0 0 680 H"). Set H to fit content + 40px padding
• Safe area: x=40 to x=640, y=40 to y=(H-40)
• Pre-built classes: t (14px), ts (12px secondary), th (14px medium 500), box, node, arr, c-{color}
• Every <text> element must carry a class (t, ts, or th)
• Use dominant-baseline="central" for vertical text centering in boxes
• Connector paths need fill="none" (SVG defaults to fill: black)
• Stroke width: 0.5px for borders and edges
• Make all nodes clickable: onclick="sendPrompt('...')"

---

Step 6: Interactive Explainer Template

For interactive explainers (sliders, live calculations, inline SVG):

<div style="display: flex; align-items: center; gap: 12px; margin: 0 0 1.5rem;">
  <label style="font-size: 14px; color: var(--color-text-secondary);">Years</label>
  <input type="range" min="1" max="40" value="20" id="years" style="flex: 1;" />
  <span style="font-size: 14px; font-weight: 500; min-width: 24px;" id="years-out">20</span>
</div>

<div style="display: flex; align-items: baseline; gap: 8px; margin: 0 0 1.5rem;">
  <span style="font-size: 14px; color: var(--color-text-secondary);">$1,000 →</span>
  <span style="font-size: 24px; font-weight: 500;" id="result">$3,870</span>
</div>

<div style="margin: 2rem 0; position: relative; height: 240px;">
  <canvas id="chart"></canvas>
</div>

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/4.5.1/chart.umd.js" onload="initChart()"></script>
<script>
function initChart() {
  // slider logic, chart rendering, sendPrompt() for follow-ups
}
if (window.Chart) initChart();
</script>

Use sendPrompt() to let users ask follow-ups: sendPrompt('What if I increase the rate to 10%?')

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Step 7: Respond to the User

After rendering the widget, briefly explain:

1. What the widget shows
2. How to interact with it (which controls do what)
3. One key insight from the data

Keep it concise — the widget speaks for itself.

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Reference Files

• references/design_system.md — Complete color palette (9 ramps × 7 stops), CSS variables, UI component patterns, metric cards, layout rules
• references/svg_and_diagrams.md — SVG viewBox setup, font calibration, pre-built classes, flowchart/structural/illustrative diagram patterns with examples
• references/chart_js.md — Chart.js configuration, script load ordering, canvas sizing, legend patterns, dashboard layout

Read the relevant reference file when you need specific design tokens, SVG coordinate math, or Chart.js configuration details.