pptx-html-fidelity-audit

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):

  <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.