Html2pptx

---
name: html2pptx
description: "Convert HTML slides into native PowerPoint elements. Triggers: HTML to PPTX, convert HTML slides, html2pptx."
---

# HTML to PPTX Skill

Convert HTML slides into native PowerPoint elements with accurate positioning.
Covers: HTML→native PPTX conversion (text, images, shapes, lists), screenshot fallback.
For programmatic slide creation without HTML, see [pptx skill](../pptx/SKILL.md).

---

## Quick Reference

| Task | Tool |
|------|------|
| Convert (native) | `require("./scripts/html2pptx.cjs")` — library, not CLI |
| Convert (screenshot) | `node scripts/convert.mjs slide.html [output.pptx] [--layout 16x9\|4x3]` |
| Batch convert | `node scripts/batch.mjs slide-01.html slide-02.html [--output deck.pptx] [--layout 16x9\|4x3]` |

---

## How It Works

```
HTML file → Playwright render → page.evaluate():
  ├── body background extraction (image/color)
  ├── DOM element traversal
  │   ├── <div> + background/border → shape element
  │   ├── <img> → image element
  │   ├── <p>, <h1>-<h6> → text element + inline formatting
  │   ├── <ul>, <ol> → bullet list element
  │   └── .placeholder → { x, y, w, h } for addChart() etc.
  └── validation (overflow, dimension mismatch)
→ PptxGenJS addText/addImage/addShape()
→ { slide, placeholders }
```

---

## Usage

### Single Slide

```javascript
const pptxgen = require("pptxgenjs");
const html2pptx = require("./scripts/html2pptx.cjs");

(async () => {
  const pres = new pptxgen();
  pres.layout = "LAYOUT_16x9"; // must match HTML body dimensions

  const { slide, placeholders } = await html2pptx("slide.html", pres);

  if (placeholders.length > 0) {
    slide.addChart(pres.charts.LINE, chartData, placeholders[0]);
  }

  await pres.writeFile({ fileName: "output.pptx" });
})();
```

### Batch

```javascript
const path = require("path");
const pptxgen = require("pptxgenjs");
const html2pptx = require("./scripts/html2pptx.cjs");

(async () => {
  const pres = new pptxgen();
  pres.layout = "LAYOUT_16x9";

  const slides = ["slide-01.html", "slide-02.html", "slide-03.html"];
  for (const file of slides) {
    await html2pptx(path.join(__dirname, file), pres);
  }
  await pres.writeFile({ fileName: "deck.pptx" });
})();
```

### Screenshot Fallback

When CSS is too complex for native conversion:

```bash
node scripts/convert.mjs slide.html output.pptx
```

Renders HTML as a full-page screenshot embedded as a single image. Tradeoff: pixel-perfect visuals, but text is not selectable/editable.

---

## HTML Authoring Rules

### Required

- `<body>` must have explicit `width` and `height` matching the presentation layout:
  - 16:9 → `width: 960px; height: 540px` (10" × 5.625" at 96 DPI)
  - 4:3 → `width: 960px; height: 720px` (10" × 7.5" at 96 DPI)
- All text in `<p>`, `<h1>`–`<h6>`, `<ul>`, or `<ol>` — bare text in `<div>` is silently dropped

### Supported CSS → PPTX Mapping

| CSS Property | PPTX Mapping | Notes |
|-------------|-------------|-------|
| `background-color` | shape fill | On `<div>` only |
| `border` (uniform) | shape line | Same width all 4 sides |
| `border` (partial) | line shapes | Individual lines per side |
| `border-radius` | `rectRadius` | px, pt, or % |
| `box-shadow` | shadow prop | Outer only |
| `transform: rotate()` | `rotate` prop | Degrees, matrix parsed |
| `writing-mode` | 90°/270° | `vertical-rl` = 90° |
| `text-transform` | applied directly | uppercase, lowercase, capitalize |
| `<b>`, `<strong>` | `bold: true` | |
| `<i>`, `<em>` | `italic: true` | |
| `<u>` | `underline: true` | |

### Unsupported CSS

| CSS Property | Workaround |
|-------------|-----------|
| CSS gradients | Rasterize to PNG with Sharp |
| Background images on `<div>` | Use `<img>` or slide-level background |
| `box-shadow: inset` | Not supported in PowerPoint |
| Margins on inline `<span>` | Use padding on parent |
| Bare text in `<div>` | Wrap in `<p>` or heading tags |

---

## Placeholders

Add `class="placeholder"` to extract position without rendering:

```html
<div class="placeholder" id="chart-area"
     style="position: absolute; left: 100px; top: 200px; width: 400px; height: 300px;">
</div>
```

Returns: `{ id: "chart-area", x: 1.04, y: 2.08, w: 4.17, h: 3.12 }`

Use coordinates to place charts, external images, or other programmatic content.

---

## Validation Errors

| Check | Error Pattern |
|-------|--------------|
| Content overflow | "HTML content overflows body by Xpt..." |
| Dimension mismatch | "HTML dimensions don't match presentation layout..." |
| Text too close to bottom | "Text box ends too close to bottom edge..." |
| CSS gradients | "CSS gradients are not supported..." |
| Background images on div | "Background images on DIV elements..." |
| Bare text in div | "DIV element contains unwrapped text..." |
| Styling on text elements | "Text element has background/border/shadow..." |
| Manual bullet symbols | "Text element starts with bullet symbol..." |
| Margins on inline spans | "Inline element has margin-left..." |

All errors are collected and thrown together.

---

## Anti-Patterns

| Instead of... | Do this | Why |
|--------------|---------|-----|
| Bare text in `<div>` | Wrap in `<p>`, `<h1>`–`<h6>`, `<ul>` | Bare text is silently dropped |
| Background/border on `<p>`, `<h>` | Move styling to parent `<div>` | Only `<div>` maps to PPTX shapes |
| CSS gradients | Rasterize to PNG first | No PPTX gradient equivalent |
| Manual bullet chars (`• Item`) | Use `<ul><li>Item</li></ul>` | Proper PPTX bullets with indentation |
| Margins on `<span>` | Use padding on parent | Inline margins ignored in PowerPoint |
| Omitting body width/height | Set explicit dimensions | Converter can't infer slide size |

---

## Dependencies

```bash
npm install pptxgenjs playwright sharp
npx playwright install chromium
```

On macOS, `convert.mjs`/`html2pptx.cjs` use `channel: "chrome"` (system Chrome). If Chrome is unavailable, remove `launchOptions.channel` to use Playwright's bundled Chromium.

---

## QA Workflow

```bash
# 1. Convert
node scripts/batch.mjs slide-*.html --output deck.pptx

# 2. Visual check
soffice --headless --convert-to pdf deck.pptx
pdftoppm -jpeg -r 150 deck.pdf slide

# 3. Compare HTML vs PPTX output side-by-side
```

Checklist:
- [ ] All text elements converted (no bare text dropped)
- [ ] Shape fills match HTML background colors
- [ ] Border rendering correct
- [ ] Image positions match HTML layout
- [ ] Placeholder coordinates returned correctly
- [ ] No validation errors thrown
- [ ] Text selectable in PowerPoint (not rasterized)