pptx-html-fidelity-audit

The saved excerpt is a snapshot from when this skill was listed. The external source remains the complete and most current version.

---
name: pptx-html-fidelity-audit
description: Audit a python-pptx export against its source HTML deck, identify layout/content drift (footer overflow, cropped content, missing italic/em, lost styling, off-rhythm spacing), and re-export with strict footer-rail + cursor-flow layout discipline. Use this skill whenever the user has a .pptx that was generated from an HTML slide deck and asks to compare/audit/verify/fix the export — including phrases like "compare ppt with html", "fidelity audit", "fix the pptx", "ppt is cut off", "footer overlap", "italic missing in pptx", "re-export the deck", "pptx-html-fidelity-audit", or any case where a python-pptx → HTML round-trip needs verification or repair. Also trigger when the user shows you a deck.html and a deck.pptx side by side and is debugging visual differences.
triggers:
  - "pptx fidelity"
  - "pptx audit"
  - "ppt 跑掉"
  - "字型不對"
  - "footer overlap"
  - "verify pptx"
  - "html to pptx"
od:
  mode: utility
  scenario: engineering
---

# PPTX ↔ HTML Fidelity Audit

A repeatable workflow for catching the ways a `python-pptx` export silently drifts from its HTML source — and fixing them with a layout discipline that prevents the same regressions on the next pass.

## When this skill applies

The user has:

- A source HTML slide deck (typically a single-file deck with `<section class="slide">` blocks):

  ```html
  <section class="slide light">
    <div class="chrome">2026 · Q2 review</div>
    <span class="kicker">Pillar 03</span>
    <h2 class="h-xl">Shipping <em>velocity</em> doubled</h2>
    <p class="lead">…</p>
    <div class="foot">page 5 / 14</div>
  </section>
  ```

- A PPTX file generated from that deck via python-pptx (or similar).
- A suspicion (or visible evidence) that the PPTX doesn't match the HTML — text bleeding into the footer, italic words gone flat, hero slides not centered, sections cropped, tag styling lost.

If the user only has *one* of those two artifacts, this skill doesn't apply yet — first generate the missing one, or ask the user to provide it.

## Why this is hard (and why a skill helps)

PPTX is a fixed-canvas, absolute-positioned medium. HTML is a fluid, flow-based medium. A naive python-pptx export pins each block at hand-picked `(top, left)` coordinates, which works for the *first slide it was tested on* and silently fails for every other slide whose content has different intrinsic height. The result is the most common drift modes:

1. **Footer overflow** — content's `top + height` crosses into the footer row.
2. **Off-canvas content** — bottom of last block exceeds `7.5"` (16:9 canvas).
3. **Italic loss** — `<em>` in HTML never gets `run.font.italic = True`.
4. **Hero slides not centered** — vertical-stack slides use `MARGIN_TOP` instead of computing center.
5. **Box bounds intruding** — the text fits, but the *shape's bounding box* is oversized and visually crosses the rail.
6. **Tag/styling loss** — colored chrome rows, kicker uppercase tracking, mono-vs-serif assignments quietly fall back to defaults.

Every one of these is a *layout discipline* problem, not a content problem. Once you adopt the discipline, they stop happening.

---

## Workflow

The audit is five steps. Don't skip any of them — the discipline only works if the audit produces a real list of issues to drive the re-export. A fix-without-audit pass tends to leave half the issues alive.

### Step 1 — Extract ground truth from the PPTX

Run `scripts/extract_pptx.py <path-to.pptx> > pptx_dump.json`. The script walks every shape on every slide and dumps text, position (`top` / `left`), size (`width` / `height`), and per-run typography (font name, size pt, bold, italic, color). This is the *actual* state of the export — don't trust the export script's intent, trust the dump.

For 14-slide decks, the dump is ~30–60 KB and human-readable.

### Step 2 — Walk the HTML structure

Read the source HTML and enumerate `<section class="slide">` blocks. For each, note:

- The slide's theme (`l