| name | pptx-dotnet |
| description | Create, edit, and analyze PowerPoint presentations (.pptx) using C# and .NET 8. Use when the user requests PPTX work AND specifies C#/.NET, or when the project context is .NET/C#. Supports: (1) Creating presentations from scratch via HtmlBuild (write HTML/CSS, Playwright extracts layout, OpenXml SDK generates native PPTX), (2) Editing existing presentations via template inventory/replace workflow, (3) Slide rearrangement and duplication. |
PPTX (.NET)
Create beautiful presentations using HTML/CSS and .NET. The LLM writes HTML slides, Playwright renders them in headless Chromium to extract precise layout, and the OpenXml SDK generates native PPTX with editable text and shapes. No visual validation loop needed — what you write in HTML is what you get in PowerPoint.
Workflow Decision Tree
- Create from scratch → HtmlBuild workflow (Section A) — write HTML/CSS slides
- Create from template → Inventory/Replace workflow (Section B)
- Rearrange/duplicate slides → Rearrange tool (Section C)
A. Create from Scratch — HtmlBuild
Write one HTML file per slide. Playwright renders it in headless Chromium, extracts element positions and computed styles from the DOM, and converts them to native OpenXml shapes. The output is a real PPTX with editable text — not screenshots.
A1. Choose a theme
Select from references/themes.json. Preview at assets/theme-previews.png.
| Theme | Style | Best for |
|---|
| midnight | Dark blue, cyan accents | Tech, corporate, data |
| ocean | Teal/marine | Healthcare, biotech, science |
| arctic | Clean white/ice blue | Clinical, minimal, regulatory |
| ember | Dark with red/orange | Energy, urgency, alerts |
| forest | Deep green | Sustainability, growth |
| slate | Professional gray | Corporate, finance |
| ivory | Warm cream/gold | Academic, classical |
| aurora | Purple/violet | Innovation, creative |
| copper | Earth tones | Consulting, strategy |
| glacier | Ice blue/silver | Analytics, data science |
| obsidian | Near-black, neon accents | Technical, dev |
| sandstone | Warm neutral | Community, education |
Load the theme colors and use them consistently across all slides.
A2. Write HTML slides
Each slide is a standalone HTML file. The <body> dimensions must match the aspect ratio:
| Aspect | Body style |
|---|
| 16:9 | width: 720pt; height: 405pt |
| 4:3 | width: 720pt; height: 540pt |
| 16:10 | width: 720pt; height: 450pt |
Slide template
<!DOCTYPE html>
<html><head><meta charset="utf-8"></head>
<body style="width: 720pt; height: 405pt; margin: 0; padding: 0; font-family: Arial, sans-serif; background: #F8FAFC;">
<div style="position: absolute; top: 0; left: 0; right: 0; height: 4pt; background: #0369A1;"></div>
<h1 style="position: absolute; top: 22pt; left: 45pt; width: 400pt; font-size: 22pt; color: #0F172A; margin: 0;">
Slide Title Here
</h1>
<div style="position: absolute; top: 50pt; left: 45pt; width: 50pt; height: 3pt; background: #0EA5E9;"></div>
</body>
</html>
A3. HTML-to-PPTX element mapping
| HTML | PPTX result | Notes |
|---|
<p>, <h1>–<h6> | Text shape | ALL text must be in these tags |
<ul>, <ol> with <li> | Bulleted/numbered list | Never use manual bullet symbols (•, -, *) |
<b>, <i>, <u>, <span> | Rich text runs | Inline formatting within a text element |
<div> with background | Filled rectangle | Supports border-radius, box-shadow |
<div> with border | Rectangle with outline, or line shapes for partial borders | |
<img> | Embedded image | Use absolute file paths |
<div class="placeholder"> | Reserved position | Returns {id, x, y, w, h} for charts |
What does NOT convert
- ❌ CSS gradients (
linear-gradient, radial-gradient) — rasterize as PNG first
- ❌ Text directly in
<div> — will silently disappear. Always wrap in <p> or heading
- ❌ Backgrounds/borders on text elements (
<p>, <h1>, <ul>) — only <div> supports these
- ❌ Margins on inline
<span>, <b>, <i> — not supported in PowerPoint text runs
- ❌ Inset box-shadows — only outer shadows convert
- ❌ Custom fonts — use web-safe only: Arial, Georgia, Verdana, Tahoma, Trebuchet MS, Times New Roman, Impact, Courier New
A4. Critical design rules
These rules prevent the layout problems that occur when browser rendering differs from PowerPoint text rendering. Follow them strictly.
Typography
| Element | Max font size | Notes |
|---|
| Slide title | 22pt | Bold, one line preferred |
| Section header | 14–16pt | Bold |
| Body text / bullets | 9–12pt | Regular weight |
| Stat numbers | 26–30pt | Bold, inside cards |
| Stat labels | 9–10pt | Below the number |
| Footnotes / sources | 8–9pt | Muted color |
| Card headers | 12pt | Bold, colored |
Never use titles larger than 22pt on content slides. Title slides may use up to 30pt.
Layout
- Margins: Minimum 45pt from all edges for content
- Title area: Top 22pt to 55pt (title + underline accent)
- Content area: 65pt to 290pt — this is the safe working zone
- Bottom 30%: Keep clear or use only for footnotes/source text
- Card spacing: Minimum 15pt gap between cards
- Card rows: Maximum 2 rows of cards per slide
Shapes and text — the critical rule
Never nest absolute-positioned text inside absolute-positioned divs for cards.
Instead, place the background shape and the text as separate sibling elements at the body level:
<div style="position: absolute; top: 65pt; left: 45pt; width: 200pt; height: 70pt;
background: #FFFFFF; border-radius: 5pt; border-left: 4pt solid #DC2626;
box-shadow: 1px 2px 4px rgba(0,0,0,0.08);"></div>
<p style="position: absolute; top: 73pt; left: 62pt; width: 170pt;
font-size: 26pt; color: #DC2626; margin: 0; font-weight: bold;">1,420</p>
<p style="position: absolute; top: 105pt; left: 62pt; width: 170pt;
font-size: 10pt; color: #64748B; margin: 0;">Missed visits per year</p>
<div style="position: absolute; top: 65pt; left: 45pt; width: 200pt; height: 70pt;
background: #FFFFFF; border-radius: 5pt;">
<p style="position: absolute; top: 10pt; left: 15pt; font-size: 26pt;">1,420</p>
<p style="position: absolute; top: 45pt; left: 15pt; font-size: 10pt;">Missed visits</p>
</div>
Callout boxes
<div style="position: absolute; top: 210pt; left: 45pt; width: 630pt; height: 55pt;
background: #EFF6FF; border-radius: 5pt; border-left: 4pt solid #0369A1;"></div>
<p style="position: absolute; top: 220pt; left: 62pt; width: 598pt;
font-size: 11pt; color: #1E293B; margin: 0; line-height: 1.5;">
<b>Key finding:</b> Your insight text here.
</p>
Stat cards (3-across)
<div style="position: absolute; top: 65pt; left: 45pt; width: 200pt; height: 75pt;
background: #0369A1; border-radius: 5pt;"></div>
<p style="position: absolute; top: 72pt; left: 60pt; width: 170pt;
font-size: 28pt; color: #FFFFFF; margin: 0; font-weight: bold;">10%</p>
<p style="position: absolute; top: 106pt; left: 60pt; width: 170pt;
font-size: 9pt; color: #BAE6FD; margin: 0;">Target no-show rate</p>
<div style="position: absolute; top: 65pt; left: 260pt; width: 200pt; height: 75pt;
background: #0369A1; border-radius: 5pt;"></div>
<p style="position: absolute; top: 72pt; left: 275pt; width: 170pt;
font-size: 28pt; color: #FFFFFF; margin: 0; font-weight: bold;">640</p>
<p style="position: absolute; top: 106pt; left: 275pt; width: 170pt;
font-size: 9pt; color: #BAE6FD; margin: 0;">Appointments recovered</p>
<div style="position: absolute; top: 65pt; left: 475pt; width: 200pt; height: 75pt;
background: #0369A1; border-radius: 5pt;"></div>
<p style="position: absolute; top: 72pt; left: 490pt; width: 170pt;
font-size: 28pt; color: #FFFFFF; margin: 0; font-weight: bold;">$170K</p>
<p style="position: absolute; top: 106pt; left: 490pt; width: 170pt;
font-size: 9pt; color: #BAE6FD; margin: 0;">Revenue recovered</p>
Two-column content cards (2×2 grid)
<div style="position: absolute; top: 65pt; left: 45pt; width: 310pt; height: 100pt;
background: #FFFFFF; border-radius: 5pt;
box-shadow: 1px 2px 4px rgba(0,0,0,0.06);"></div>
<p style="position: absolute; top: 72pt; left: 58pt; width: 280pt;
font-size: 12pt; color: #0369A1; margin: 0; font-weight: bold;">1. Card Title</p>
<ul style="position: absolute; top: 90pt; left: 58pt; width: 280pt;
font-size: 9pt; color: #334155; line-height: 1.8; padding-left: 10pt;">
<li>Point one</li>
<li>Point two</li>
<li>Point three</li>
</ul>
<div style="position: absolute; top: 65pt; left: 370pt; width: 310pt; height: 100pt;
background: #FFFFFF; border-radius: 5pt;
box-shadow: 1px 2px 4px rgba(0,0,0,0.06);"></div>
<p style="position: absolute; top: 72pt; left: 383pt; width: 280pt;
font-size: 12pt; color: #0369A1; margin: 0; font-weight: bold;">2. Card Title</p>
<ul style="position: absolute; top: 90pt; left: 383pt; width: 280pt;
font-size: 9pt; color: #334155; line-height: 1.8; padding-left: 10pt;">
<li>Point one</li>
<li>Point two</li>
<li>Point three</li>
</ul>
A5. Build the PPTX
Docker (recommended) — all dependencies baked in, nothing to install:
docker run --rm -v /path/to/slides:/data ghcr.io/drpedapati/htmlbuild \
slide1.html slide2.html slide3.html output.pptx [--aspect 16:9|4:3|16:10]
Local (requires .NET 8 SDK):
cd $SKILL_DIR/scripts/HtmlBuild
dotnet run -- slide1.html slide2.html slide3.html output.pptx [--aspect 16:9|4:3|16:10]
The builder:
- Renders each HTML in headless Chromium via Playwright
- Extracts all element positions and computed styles from the DOM
- Validates: overflow, unsupported CSS, unwrapped text, manual bullets
- Generates native PPTX with editable text shapes — not rasterized images
No visual validation loop. The HTML is the source of truth.
A6. Slide dimensions reference
| Aspect | Width | Height | Body style |
|---|
| 16:9 | 10" | 5.625" | 720pt × 405pt |
| 4:3 | 10" | 7.5" | 720pt × 540pt |
| 16:10 | 10" | 6.25" | 720pt × 450pt |
B. Create from Template
Use an existing .pptx as a design template. Extract its structure, rearrange slides, replace text.
B1. Analyze template
cd $SKILL_DIR/scripts/Inventory
dotnet run -- template.pptx template-inventory.json
cd $SKILL_DIR/scripts/Validate
dotnet run -- template.pptx --outdir /tmp/template-slides
Read each PNG. Map every slide to its purpose.
B2. Rearrange slides
cd $SKILL_DIR/scripts/Rearrange
dotnet run -- template.pptx working.pptx 0,3,3,7,12,12,15
Comma-separated 0-based indices. Duplicates allowed. Unlisted slides deleted.
B3. Extract and replace text
cd $SKILL_DIR/scripts/Inventory
dotnet run -- working.pptx text-inventory.json
cd $SKILL_DIR/scripts/Replace
dotnet run -- working.pptx replacement-text.json output.pptx
Replacement JSON matches the inventory structure. See B5 below for format.
B4. Inventory JSON structure
{
"slide-0": {
"shape-0": {
"position": {"left_in": 0.5, "top_in": 0.5, "width_in": 9.0, "height_in": 1.0},
"paragraphs": [
{"text": "Original Title", "font_size": 36, "bold": true, "color": "000000"}
]
}
}
}
B5. Replacement JSON
{
"slide-0": {
"shape-0": {
"paragraphs": [
{"text": "New Title", "font_size": 36, "bold": true, "color": "1a1a2e",
"alignment": "CENTER", "font_name": "Arial"}
]
}
}
}
Paragraph properties: text, bullet (bool), level, alignment (CENTER/RIGHT/JUSTIFY), space_before/space_after (pt), font_name, font_size, bold, italic, underline, color (hex without #), theme_color.
C. Rearrange Slides
cd $SKILL_DIR/scripts/Rearrange
dotnet run -- input.pptx output.pptx 0,1,1,3,5
- Comma-separated 0-based slide indices
- Repeated indices = duplicated slides
- Unlisted slides are deleted
Tools Reference
| Tool | Purpose | Usage |
|---|
| HtmlBuild | HTML → PPTX | docker run --rm -v .:/data ghcr.io/drpedapati/htmlbuild slide1.html output.pptx |
| Inventory | Extract text map | dotnet run -- input.pptx output.json [--issues-only] |
| Replace | Swap text content | dotnet run -- input.pptx replacements.json output.pptx |
| Rearrange | Reorder slides | dotnet run -- input.pptx output.pptx 0,3,3,7 |
| Validate | Render to PNG | dotnet run -- input.pptx [--outdir dir] [--width N] |
| DirectBuild | JSON → PPTX (legacy) | dotnet run -- slides.json output.pptx [--aspect 16:9] |
Docker
The ghcr.io/drpedapati/htmlbuild image packages everything — .NET 8 runtime, headless Chromium, OpenXml SDK, scaffold templates. No local dependencies needed.
docker run --rm -v /path/to/slides:/data ghcr.io/drpedapati/htmlbuild \
slide1.html slide2.html slide3.html output.pptx
cd skills/pptx-dotnet
docker build -t htmlbuild .
Dependencies (local dev only)
.NET SDK 8.0 or later. Headless Chromium (auto-installed by Playwright on first run).
NuGet packages (all signed, restored automatically):
DocumentFormat.OpenXml — Microsoft Open XML SDKMicrosoft.Playwright — headless browser for HTML rendering (HtmlBuild only)SkiaSharp — cross-platform 2D graphics (Validate only)
