lidge-jun 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.
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
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
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:
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 explicitwidthandheightmatching 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)
- 16:9 →
- 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:
<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
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
# 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)