Skills
skills/thomasrohde/pptx-cli/pptx-deck-builder

pptx-deck-builder

SKILL.md

pptx + excal Deck Builder

Build template-bound, validated PowerPoint decks with professional diagrams. This skill combines two CLI tools (pptx for slide generation, excal for diagrams) with consulting-grade presentation principles.

When to read the reference files

  • references/pptx-workflow.md — Read when you need the full pptx CLI command reference, manifest structure, placeholder details, deck spec format, error codes, or image-handling workarounds.
  • references/excal-diagrams.md — Read when you need to create Excalidraw diagrams, render them to PNG, or understand the scene JSON format.
  • references/mckinsey-style.md — Read when the user asks for consulting-style, executive, strategy, or McKinsey-style presentations. Also read when you need guidance on action titles, storyline structure, slide archetypes, or the Pyramid Principle.

Core workflow

Every deck project follows this sequence. Do not skip steps.

Step 0 — Think before building

Before touching any tool, resolve the presentation's purpose:

  1. What decision or outcome is this deck driving?
  2. What is the single governing thought or recommendation?
  3. What are the 3-5 supporting arguments?
  4. What evidence proves each argument?

If the user's request is vague, ask clarifying questions. A deck without a clear purpose becomes a collection of slides instead of an argument.

For consulting-style decks, write a ghost deck first — a title-only outline where each slide title states the takeaway (not the topic). The titles alone should tell a coherent story. See references/mckinsey-style.md.

Step 1 — Initialize the manifest (one-time setup)

Check if a manifest package already exists. If not, initialize from the template. Do not assume a PowerPoint template exists; ask the user for the actual template path when it is not already present in the workspace:

pptx init <template.pptx> --out ./corp-template --format json

Then run the doctor to verify compatibility:

pptx doctor --manifest ./corp-template --format json

Step 2 — Discover layouts and placeholders

List available layouts, then inspect placeholders for the ones you plan to use:

pptx layouts list --manifest ./corp-template --format json
pptx placeholders list <layout-id> --manifest ./corp-template --format json

Read-only commands can run in parallel for speed. Key information per placeholder:

  • logical_name — The key to use in your spec (e.g., title, content_1)
  • placeholder_type — title, body, object, or picture
  • supported_content_types — What it accepts (text, markdown-text, image, table, chart)
  • required — Whether it must be filled
  • estimated_text_capacity — Preferred normalized guidance for text-capable placeholders. Read max_lines first, then check confidence, source, and font_size_pt.
  • text_defaults — Raw extracted placeholder hints such as suggested font size or explicit max_lines from the template text
  • left_emu, top_emu, width_emu, height_emu — The actual geometry. Treat width_emu and height_emu as hard constraints for how much content the placeholder can realistically hold.

For slide drafting, prefer estimated_text_capacity.max_lines over parsing text_defaults.max_lines directly. Treat it as guidance, not a hard rule: stay at or below the line estimate when possible, and be more conservative when confidence is low.

Respect placeholder size in every content decision:

  • Text: do not write beyond the likely line budget for the box. If the message does not fit, tighten the wording or choose a layout with a larger text area.
  • Images and diagrams: match the placeholder aspect ratio and expected visual density to the available width and height.
  • Tables and charts: reduce rows, columns, labels, or series when the placeholder is small. Prefer a larger layout over forcing dense content into a small box.

Also inspect theme colors and assets if you need to match the visual identity:

pptx theme show --manifest ./corp-template --format json
pptx assets list --manifest ./corp-template --format json

Step 3 — Create diagrams with excal (if needed)

When the deck needs diagrams, flowcharts, or visual explanations, create them as Excalidraw scenes and render to PNG.

Critical: match the placeholder aspect ratio. Before designing a diagram, check the target placeholder's dimensions in EMUs (from the placeholders command). Calculate the aspect ratio and design the diagram to match.

For a picture placeholder that is 6642100 x 5514313 EMU (~1.2:1), design a diagram roughly 540px wide x 450px tall. A mismatch causes cropping or letterboxing.

# Create the .excalidraw file, then:
excal validate diagrams/my-diagram.excalidraw
excal render diagrams/my-diagram.excalidraw --outDir ./out/diagrams --png --scale 4 --no-background

Use --no-background for transparent backgrounds that blend with slide backgrounds. Use --scale 4 for crisp output — scale 2 looks blurry on large slide placeholders because the pixel density is too low for the physical size. Scale 4 ensures diagrams stay sharp even on high-DPI displays and when projected.

Match the template's visual identity. Diagrams should feel like they belong on the slide, not like foreign objects pasted in. Two things matter most:

  1. Use fontFamily: 1 (Excalidraw's hand-drawn style) for diagram text. This gives a clean whiteboard aesthetic that contrasts well with formal slide typography and looks intentional rather than mismatched.

  2. Pull colors from the template theme. Run pptx theme show --manifest ./corp-template --format json and use the accent colors for fills and strokes. Common mapping:

    • Primary elements → accent1 (e.g., #003778)
    • Secondary elements → accent2 (e.g., #4673C3)
    • Tertiary/subtle → accent3 (e.g., #87AAE1)
    • Success/positive → #087f5b (green)
    • Labels/muted → #868e96 (gray)

    Avoid arbitrary colors — diagrams that use theme colors integrate seamlessly with the slide's color palette.

Keep elements away from frame edges. Text and shapes positioned within 10px of the frame boundary may be clipped during PNG export. Use at least a 15px margin on all sides of the frame for safe rendering.

See references/excal-diagrams.md for the full Excalidraw scene format and element types.

Step 4 — Write the deck spec

Create a YAML file mapping layouts to content:

manifest: ./corp-template
metadata:
  title: "Presentation Title"
  author: "Author Name"
slides:
  - layout: layout-id
    content:
      title: "Action title stating the takeaway"
      subtitle: "Optional context"
      content_1: |
        - Bullet point one
        - Bullet point two
      source: "Source: Data attribution"
    notes: |
      # Speaker notes

      - Open with the takeaway before reading the slide
      - Keep timing to under 90 seconds

  - layout: picture-layout-id
    content:
      title: "Slide title"
      picture:
        kind: image
        path: out/diagrams/my-diagram.png
      content_1: |
        Supporting text alongside the image

Content value formats:

  • Plain string → treated as text
  • Multi-line YAML block scalar with markdown-looking content (headings, lists, ordered items) → auto-detected as markdown-text
  • @notes.md via --set key=@notes.md or { kind: "markdown-text", value: "..." } → markdown parsed with headings, lists, inline emphasis, and light presentation-aware spacing
  • Slide-level speaker notes → notes: | in the deck spec, or pptx slide create --notes/--notes-file for single-slide generation
  • { kind: "image", path: "path/to/file.png" } → image insertion
  • { kind: "table", columns: [...], rows: [[...], ...] } → table
  • { kind: "chart", chart_type: "column_clustered", categories: [...], series: [{name: "...", values: [...]}] } → chart

For markdown-heavy placeholders, prefer explicit kind: markdown-text when you want unambiguous behavior. The current renderer preserves bold, italic, inline code, bullets, nested bullets, ordered lists, and light block spacing, but it does not attempt full document-layout fidelity.

Section spacing in markdown content: When a placeholder contains multiple sections (e.g., bold heading + bullets, then another bold heading + bullets), add a blank line between sections to create visual breathing room. Without it, consecutive sections run together with minimal spacing.

Step 5 — Build and validate

pptx deck build --manifest ./corp-template --spec deck.yaml --out ./out/deck.pptx --format json
pptx validate --manifest ./corp-template --deck ./out/deck.pptx --strict --format json

Always validate with --strict. Fix any issues and rebuild. If the output file is locked (open in PowerPoint), write to a new filename.

Use --dry-run on build to preview without writing files.

Image handling

Image scaling — fit vs crop

Picture placeholders should already advertise image in supported_content_types. Do not patch manifest.yaml unless inspection output proves the template contract is actually wrong.

The current build behavior defaults to image_fit: fit, which preserves the full image inside the placeholder. Use image_fit: cover when you explicitly want crop-to-fill behavior.

slides:
  - layout: picture-layout-id
    content:
      title: Workflow
      picture:
        kind: image
        path: out/diagrams/workflow.png
        image_fit: fit

Slide writing principles

These apply to every deck, not just consulting-style ones.

Action titles, not topic labels

Every slide title should state the takeaway — what the audience should conclude — not just name the topic.

  • Bad: "Market Overview"
  • Good: "Nordic retail margins will remain under pressure through 2027"

One slide, one message

If a slide has two insights, split it into two slides. The body must prove the headline.

Respect placeholder geometry

Never treat placeholder size as flexible. The template geometry is part of the contract.

  • If text exceeds the placeholder's likely capacity, shorten it or split it.
  • If a table or chart needs more room, switch to a layout with a larger object placeholder.
  • If a diagram becomes unreadable at the placeholder's size, simplify the diagram rather than shrinking text and shapes until they are illegible.

Source attribution

Data-driven slides need source lines. Use the source placeholder when available.

Storyline coherence

A reader should be able to read only the slide titles, in order, and understand the full argument.

For full consulting-style guidance including the Pyramid Principle, MECE structuring, ghost decks, slide archetypes, and executive summary construction, read references/mckinsey-style.md.

Layout selection guide

Match content to the right layout:

Content type Suggested layout patterns
Opening / title (no image) front-page-title-and-pattern layouts
Opening / title (with image) front-page-title-and-picture layouts (see Background image warning below)
Agenda / TOC agenda layouts (one item per line — see Agenda formatting below)
Section divider breaker layouts
Single topic with bullets title-and-content
Side-by-side comparison two-contents
Topic with description header title-description-and-content
Image with explanation picture-right-text-and-box (or similar)
Minimal / custom title-only or blank-with-logo
Closing end-slide layouts

When a template has numbered variants (e.g., 1-title-and-content, 2-title-description-and-content), inspect the placeholders of each to understand the differences. Numbered variants often differ in placeholder arrangement, background color, or description fields.

Background image warning — front-page-title-and-picture layouts

On front-page-title-and-picture layouts, the picture placeholder spans the full slide and the title/subtitle render on top of the image. This means:

  • Use abstract, low-detail images only — blurred photos, gradients, subtle textures, or simple geometric shapes.
  • Never use information-dense diagrams (with text labels, data, or fine details) as the background image. The title text will collide with diagram labels, making both unreadable.
  • Reserve detailed diagrams for picture-right-text-and-box where the image sits alongside text, not beneath it.
  • If you must use a diagram, design it as an ambient background: large shapes only, no text, muted/faded colors at low opacity.

Agenda formatting

Agenda layouts expect one item per line, not a pipe-delimited string. The layout may auto-number items. Do not add numbered prefixes yourself.

# WRONG — renders as a single cramped line
content_1: "Foundations | Modern Patterns | Cloud-Native | Serverless"

# CORRECT — each item on its own line
content_1: |
  Foundations
  Modern Patterns
  Cloud-Native
  Serverless
  AI-Native
  What's Next

Series 2 (white) vs Series 3 (sand) layouts

When a template offers both white-background (series 2) and sand-background (series 3) variants of the same column layout:

Visual intent Use
Standard content slides Series 2 (white background)
Highlighted or callout content Series 3 (sand background)
Visual rhythm in long decks Alternate between series 2 and 3 per section

Do not mix white and sand variants within the same logical section — pick one per section and stay consistent.

Front-page variant differences

Front-page layouts with the same column count may differ in subtitle placement. For example, variant 1 may place the subtitle above the title while variant 2 places it below. Always inspect placeholders (top_emu values) to understand the visual order before authoring content.

End-slide positioning

End-slide layouts typically position the title left-of-center with the right portion of the slide empty. Keep closing titles short (1-3 words like "Thank you" or "Questions?") for visual balance.

Quick reference — common commands

# One-time setup
pptx init <template.pptx> --out ./manifest-dir --format json
pptx doctor --manifest ./manifest-dir --format json

# Inspection (safe to parallelize)
pptx layouts list --manifest ./manifest-dir --format json
pptx placeholders list <layout-id> --manifest ./manifest-dir --format json
pptx theme show --manifest ./manifest-dir --format json
pptx assets list --manifest ./manifest-dir --format json

# Single slide (quick test)
pptx slide create --manifest ./manifest-dir --layout <id> --set title="Hello" --notes-file ./speaker-notes.md --out slide.pptx

# Full deck
pptx deck build --manifest ./manifest-dir --spec deck.yaml --out deck.pptx --format json
pptx validate --manifest ./manifest-dir --deck deck.pptx --strict --format json

# Diagrams
excal validate diagram.excalidraw
excal render diagram.excalidraw --outDir ./out --png --scale 4 --no-background

# Template versioning
pptx manifest diff ./v1-manifest ./v2-manifest --format json

Error handling

All pptx commands return JSON envelopes with ok, errors, and exit codes:

Exit code Meaning
0 Success
10 Validation error (bad layout, missing placeholder, wrong content type)
20 Policy error
40 Conflict (output file exists / locked)
50 I/O error (file not found)
90 Internal error

If output file is locked (exit code 40 or PermissionError), write to a different filename — do not retry.

All excal errors also return JSON envelopes. Key codes: exit 10 for invalid scene JSON, exit 20 for render failures, exit 50 for I/O errors.

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