confidential-html-deck

Confidential HTML deck

A Claude skill for building presentation decks from confidential data without sharing that data with Claude.

Claude builds the deck as one self-contained HTML file in PowerPoint's 16:9 format. Every sensitive value (client names, revenue, KPIs, dates, deal terms) is a variable holding dummy data. You open the file in your browser, enter or import the real values, and print it to PDF. Claude only ever sees the dummy version.

How it keeps your data local

• No network. A Content Security Policy blocks every request: the deck can't load or send anything. Fonts and logos are embedded.
• Values stay in the tab. Real values live only in the browser tab's memory and are never written into the HTML. There's deliberately no "save filled deck" option.
• Visible sample data. Every slide carries a "Sample data" badge until all values are yours. Values still on their sample are outlined, and printing warns you first.
• Calculated, not typed. Totals, growth rates, shares, and wording such as "grew"/"declined" or the headline are calculated in the page. They stay correct once the real numbers are in.
• Leak checks. If an HTML file was saved from the browser after data was loaded, the deck shows a red warning and the skill's checks refuse to work from it.

The workflow

1. Brief. Tell Claude what the deck is for, the design language (colours, type, logo, layout character) and the shape of your data: how long the names are, rough magnitudes, how many rows. The skill has no house style, so every deck is designed from your brief.

2. Iterate on the design. Each version comes with a PDF preview rendered from the dummy data, shown in the chat. You give feedback on the preview without switching windows.

3. Add your data. When the design is final, open the HTML in Chrome or Edge and click Edit data:

   • type values into the form, or edit the raw JSON;
   • or Import / drag in your JSON file from last time.

   The slides update as you type. Export saves your values as JSON for the next edition.

4. Print. Click PDF. You get one page per slide at 13.33 × 7.5 in.

5. Next version. Upload only the deck HTML, never your data JSON or a filled PDF. Claude keeps the variable keys stable and lists any values that were added, renamed or removed.

The viewer

The viewer is part of every deck and is never printed.

• Edit data: values are grouped into collapsible sections, each showing how many of its values are yours. There's a filter box, and each field shows its status (sample / yours / invalid) and a formatted preview. Lists are edited as a small grid. A JSON tab lets you paste or edit everything at once.
• Strict input. Numbers are plain (1250000.5), percentages may be typed as 12.5%, and dates use a picker. Ambiguous input like 1.000 is rejected rather than guessed, so the same data always produces the same deck.
• Check: lists missing, invalid and still-sample values, undefined variables and failed calculations.
• Present (F), Export, PDF, and a light/dark switch that follows your system setting. The light/dark choice is the only thing the deck stores in your browser.

macOS note: Gatekeeper may block a downloaded .json file when you double-click it. You never need to open it: use Import or drag it onto the deck.

Install

Claude apps: download confidential-html-deck.skill from the latest release and add it in Claude's skill settings.

Claude Code: copy the skill folder into your skills directory:

git clone https://github.com/tokuhn/confidential-html-deck.git
cp -r confidential-html-deck/skills/confidential-html-deck ~/.claude/skills/

Then ask Claude for a deck with confidential data, for example: "Make a quarterly account review deck for a client. Keep all client figures as placeholders."

The skill's check scripts need Python 3. The rendering check and PDF preview also need Playwright with Chromium (pip install playwright pypdf && python -m playwright install chromium). Without Playwright, Claude runs only the static check and says there's no preview.

Try the example

examples/example-deck.html is a five-slide wireframe. It shows the mechanics (calculated headline, chart and table from a list, progress bar, wording that follows the data) and deliberately has no design. Open it in your browser and click Import with examples/example-data.json to see the slides switch to that data set. examples/example-deck-preview.pdf is the dummy-data preview Claude would show you in the chat.

All names and figures in the examples are invented.

What's in the skill

skills/confidential-html-deck/
├── SKILL.md                 instructions Claude follows
├── assets/
│   ├── deck-template.html   starting point: variables, empty design sections, runtime
│   └── example-deck.html    wireframe reference for patterns
├── references/runtime.md    types, formats, tables, charts, calculations, viewer
└── scripts/
    ├── lint_deck.py         privacy and consistency checks (stdlib only)
    ├── render_check.py      headless render with sample + stress values, PDF preview
    └── update_runtime.py    upgrades an older deck's runtime in place

Limitations

• Output is HTML and PDF. There's no editable .pptx; you change the deck by asking Claude.
• Charts are built in: bar, horizontal bar and line. Other visuals are drawn per deck with a small custom render hook.
• The PDF preview uses the fonts installed where Claude works. Typefaces that aren't embedded in the deck may look slightly different in the preview than in your browser.
• The privacy model relies on you not uploading your data JSON, a PDF printed with real data, or a deck saved from the browser after loading data. The deck and the skill warn about the last case but can't stop you from sharing a file.

License

MIT