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slides.render

The "Marp markdown → PDF/PPTX/HTML" pack. Caller hands in a Marp deck (frontmatter + ----delimited slides) and a target format; the pack invokes the Marp CLI inside the sidecar (marp --stdin --allow-local-files), streams the binary output to the artifact store, and returns the artifact key + size. The deck never touches disk inside the sidecar — input via stdin, output streamed.

For narrated video output (MP4 with TTS over each slide), see slides.narrate. For just the static deck, this is the right pack.

Inputs​

FieldTypeRequiredDefaultNotes
markdownstringyes—Marp deck. Must start with ---\nmarp: true\n--- frontmatter for the directives to apply. Slides separated by ---.
formatstringno"pdf"Closed-set: pdf, pptx, html. Picks the Marp output codec.

Outputs​

FieldTypeNotes
formatstringEcho of the chosen format.
artifact_keystring`slides.render/-deck.{pdf
sizenumberBytes.

Vault credentials needed​

None. Marp runs entirely in-sidecar.

Use it from your agent (OpenClaw chat-UI worked example)​

Prompt (sent in OpenClaw chat UI / openclaw-cli agent):

Use helmdeck__slides-render to convert this Marp markdown to PDF: "---\nmarp: true\n---\n# Hello helmdeck\n\n---\n\n# Thanks for listening". Tell me the artifact_key and the size in bytes.

Tool call (1 call, no failures):

{
  "name": "helmdeck__slides-render",
  "arguments": {
    "format": "pdf",
    "markdown": "---\nmarp: true\n---\n# Hello helmdeck\n\n---\n\n# Thanks for listening"
  }
}

Pack response (truncated):

{"pack":"slides.render","version":"v1","output":{"artifact_key":"slides.render/7d549cd238a7bc34-deck.pdf","format":"pdf","size":7902},"artifacts":[{"key":"slides.render/7d549cd238a7bc34-deck.pdf","url":"http://garage:3900/helmdeck-artifacts/slides.render/7d549cd238a7bc34-deck.pdf?X-Amz-Algorithm=AWS4-HMAC-SHA256\u0026X-Amz-Credential=GKaef177ebe9fd814dc103b84b%2F20260508%2Fgarage%2Fs3%2Faws4_request\u0026X-Amz-Date=20260508T152130Z\u0026X-Amz-Expires=900\u0026X-Amz-SignedHeaders=host\u0026X-Amz-Signature=b2f7c01cfc3a39c4365d0bd5f79dfff7d49e972497f4eff7b535b8eaccf3c544","size":7902,"content_type":"application/pdf","created_at":"2026-05-08T15:21:30.754346118Z","pack":"slides.render"}],"duration_ms":18808030860,"session_id":"586c8ee9-3529-4128-9cbf-541e0cc20de0"}

Agent's final reply:

The PDF was created successfully.

  • artifact_key: slides.render/7d549cd238a7bc34-deck.pdf
  • size: 7902 bytes

Verified via OpenClaw 2026.5.6 + helmdeck v0.9.0-dev + openrouter/openai/gpt-oss-120b on 2026-05-07 (cost: $0.0013).

Developer reference (curl)​

curl -fsS -X POST http://localhost:3000/api/v1/packs/slides.render \
  -H "Authorization: Bearer $JWT" -H 'Content-Type: application/json' \
  -d '{
    "markdown": "---\nmarp: true\n---\n# Hello helmdeck\n\n---\n\n# Thanks for listening",
    "format":   "pdf"
  }'

Response shape:

{
  "pack": "slides.render",
  "version": "v1",
  "output": {
    "format":       "pdf",
    "artifact_key": "slides.render/abc123-deck.pdf",
    "size":         98304
  }
}

Retrieve the artifact:

curl -fsS -H "Authorization: Bearer $JWT" \
  "http://localhost:3000/api/v1/artifacts/slides.render/abc123-deck.pdf" \
  -o deck.pdf

Error codes​

CodeTriggersCaptured response
invalid_inputmarkdown emptymarkdown is required
invalid_inputformat outside the closed setunsupported format "docx"; use pdf, pptx, or html
handler_failedMarp CLI exit non-zero (malformed deck, missing fonts)marp exit N: <stderr> (truncated to 1024 chars)
artifact_failedObject store write failedartifact upload failed: …

Session chaining​

Required (creates if absent). Stateless logically — the deck is in the input, the output is an artifact — but the Marp render runs inside a session sidecar. Typically not chained; one-shot.

Async behavior​

Synchronous. PDF rendering of a 10-slide deck is ~3–6s. PPTX ~5–10s. HTML ~1–2s.

Custom design (themes + CSS)​

The pack passes the deck verbatim to marp --stdin, so all Marp frontmatter directives apply — there's no schema knob for themes because the theme lives in the markdown itself.

Built-in themes​

Marp ships three themes out of the box. Pick one in the frontmatter:

---
marp: true
theme: gaia      # or: default | uncover
---

# Slide 1
ThemeLooks like
defaultClean white background, dark text. Marp's reference look.
gaiaWarm cream background, brown accents. Good for narrative decks.
uncoverHigh-contrast minimalist (black/white). Good for keynote-style decks.

Custom CSS (per-deck overrides)​

Two ways to inject custom CSS — both work because Marp processes them inline:

Frontmatter style block (preferred — keeps everything in one place):

---
marp: true
theme: gaia
style: |
  section {
    background: linear-gradient(135deg, #1a1a2e, #16213e);
    color: #f5f5f5;
  }
  h1 { color: #00d4ff; }
  code { background: #222; color: #f0a500; padding: 2px 6px; border-radius: 3px; }
---

# Custom-styled deck

Embedded <style> tag (works inside the markdown body, useful for per-slide variations):

---
marp: true
---

<style scoped>
  section { background: #fff; color: #111; }
</style>

# This slide uses scoped CSS

<style scoped> applies only to the slide it appears on; a plain <style> block applies deck-wide.

When the agent needs custom design​

For an agent driving slides.render (or slides.narrate) on the user's behalf, the pattern is: write the design into the markdown frontmatter the agent generates. The pack itself doesn't accept theme arguments — design lives in the deck. Agents handling "make this deck look like X" prompts should emit the corresponding frontmatter directives, not pass them as separate pack inputs.

Reference: https://marpit.marp.app/theme-css for the full Marp directive list.

See also​