htmlppt

A local-first visual editor and toolchain for static HTML presentations.

An agent generates one self-contained HTML deck that follows the htmldeck/v1 contract. A person opens the same file in a local visual editor, adjusts layout and copy, and exports a clean standalone HTML file, a PDF, or one PNG per slide.

No proprietary project file, no build step, no upload. The HTML file is the source of truth.

Why

• Agents write structure; people judge visuals. MCP tools create and edit semantic HTML with stable ids, while the editor gives a human direct control over position, type, color, and slide order.

• One portable file. Slides are ordinary DOM elements and styles are ordinary CSS. A deck opens in a browser, an editor, or any HTML tool without an import/export round trip.

• Local by design. The editor host binds to 127.0.0.1, requires a per-session token, and has no cloud service, account, or telemetry.

Related MCP server: PowerPoint MCP Server

Quick start

Install or run the package (from a source checkout, run npm ci && npm run build first, then use the same commands through npx htmlppt):

npx htmlppt new deck.html --title "Quarterly review" --slides 3
npx htmlppt validate deck.html
npx htmlppt open deck.html
npx htmlppt stop deck.html

htmlppt new refuses to overwrite an existing file; pass --force to replace it. --size 1600x900 sets the canvas. open prints HTMLPPT_URL=http://127.0.0.1:<port>/?token=... and opens your browser; --no-browser prints the URL only.

The printed URL carries the session token once. The browser exchanges it for an HttpOnly session cookie and lands on http://127.0.0.1:<port>/d/<deck-file-name>, which is safe to keep in history for that session. CLI and MCP output still print the tokenized bootstrap URL for automation.

Inside the editor, type a path into the path field and press Enter to switch this host to another HTML deck. Relative paths resolve against the host's working directory, quoted paths ("deck.html") and ~ home paths are accepted, and file:// URLs work too. A successful switch keeps the host, its token, and its session; the address bar becomes /d/<new-deck-name> and saves go to the new file. Use the folder button to pick a file through the standalone editor instead, which writes through the File System Access handle.

MCP setup

Add the stdio server to an MCP client:

{
  "mcpServers": {
    "htmlppt": {
      "command": "npx",
      "args": ["-y", "htmlppt", "mcp"]
    }
  }
}

With the package installed globally, "command": "htmlppt-mcp" works too. The server exposes 25 tools and the htmlppt://contract, htmlppt://authoring, and htmlppt://example resources. See docs/mcp.md for the full tool surface.

Agent workflow

1. Read the contract and authoring guidance: call get_deck_contract, or read the htmlppt://contract and htmlppt://authoring resources.

2. Create a deck with create_deck, or inspect an existing one with get_outline, read_slide, and get_element. Do not guess slide or element ids.

3. Mutate one change per tool call (set_text, set_style, add_slide, add_image, add_table, update_chart, and so on).

4. Validate with validate_deck; fix every error before continuing.

5. Hand the deck to a person with open_editor, which returns a tokenized loopback URL.

6. Export with export_deck. If a mutation returns conflict, re-read, reconcile, and retry instead of overwriting the whole file.

The CLI talks to the same files and contract and is a good fallback for scripts and exit codes.

The htmldeck/v1 contract at a glance

A minimal valid single-slide deck needs no runtime:

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>Minimal deck</title>
  <style>
    html, body { margin: 0; background: #0b0d12; }
    .slide {
      width: 1600px; height: 900px; position: relative; overflow: hidden;
      background: #f7f5ef; color: #17181c;
      font-family: Inter, ui-sans-serif, system-ui, sans-serif;
    }
    h1 { position: absolute; left: 140px; top: 180px; margin: 0; font-size: 96px; }
  </style>
</head>
<body>
  <main data-ppt-deck>
    <section class="slide" data-slide-id="s1" data-width="1600" data-height="900">
      <h1 data-ppt-el="e1">Minimal deck</h1>
      <aside data-ppt-notes hidden>Say hello and state the goal.</aside>
    </section>
  </main>
</body>
</html>

docs/contract.md covers detection, required and optional attributes, normalization, validation diagnostics, round-trip rules, and export guarantees in full.

Editor features

• Slides: add, duplicate, delete, thumbnail rail, sorter view with drag-to-reorder, slide counter, zoom.

• Text: in-place editing plus bold, italic, underline, strikethrough, color, highlight, font family, size, alignment, line height, bullet and numbered lists, links, and clear formatting.

• Objects: text boxes, shapes, images (upload or URL), tables, and charts; select or multi-select, drag, resize with snapping and alignment guides, rotate, nudge, align/distribute, group/ungroup, change stacking order, lock, hide, copy/paste/duplicate/delete, undo/redo.

• Inspector: position and size, rotation, shape fill/stroke/radius/opacity, shape text, image alt text and percentage crop, image replacement, chart JSON, slide background (color, gradient, or image), transition selection with preview, and speaker notes.

• Presenting: fullscreen play mode with authored transitions and a presenter window showing notes, the next-slide preview, and a timer, synced through BroadcastChannel.

• Theme: the editor chrome supports Light, Dark, and System. The toolbar's three-segment control persists the choice per browser origin; System follows the operating-system preference. A new host port or origin therefore starts with the default System choice because localStorage is origin-scoped. Slide content, play mode, presenter view, and the exported runtime controls keep their own styling.

• Keyboard and accessibility: shortcuts for saving, undo/redo, nudge, grouping, zoom, and presentation, plus an in-editor shortcut reference (?) and ARIA-labelled controls.

• Persistence: 800 ms autosave, live updates when the file changes externally or through MCP, a conflict banner with reload/overwrite choices, a best-effort flush on page unload, and IndexedDB crash-recovery drafts offered on the next load. Without a host, the editor falls back to an upload/download mode: File System Access writes the original file when available, otherwise Ctrl+S or Export downloads it.

Localization

The editor, play mode, presenter, and runtime controls support English, Traditional Chinese, and Simplified Chinese. The first visit follows the browser language; the toolbar language menu persists a manual choice.

Exported decks localize at view time from the viewer's browser unless the deck sets data-ppt-locale="en", "zh-Hant", or "zh-Hans" on <html>.

Export formats

Run export through the CLI, the editor toolbar (Export), or MCP:

npx htmlppt export deck.html --format html
npx htmlppt export deck.html --format pdf
npx htmlppt export deck.html --format png --out dist/png

PDF and PNG require a system Google Chrome, Microsoft Edge, or Chromium. Set HTMLPPT_CHROMIUM to an executable path when auto-discovery fails. No browser is bundled. --out is a file for HTML/PDF and a directory for PNG. PNG creates its output directory; HTML/PDF require the target file's parent directory to exist. The host toolbar writes <name>.export.html, <name>.pdf, or <name>-sN.png next to the deck inside the same confined output directory. The CLI refuses to overwrite the source deck in any format. The MCP tool resolves outDir against the deck directory, confines it there, and defaults to the deck directory.

Security model

• The editor host binds to 127.0.0.1 only and uses a random per-session token. The tokenized first visit sets an HttpOnly SameSite=Strict cookie; page and API requests accept that cookie, while CLI, MCP, and tests may continue to use Authorization: Bearer. When an Origin header is present it must be this host's loopback origin.

• Deck scripts never execute in the editor. The preview, thumbnails, sorter, and play view use sandbox="allow-same-origin" without allow-scripts.

• The renderer disables JavaScript, blocks service workers and downloads, and permits only main-frame HTTP(S) image, font, and stylesheet requests. Frames, workers, WebSockets, navigation, forms, and local-file requests are blocked.

• Host and MCP exports stay inside the deck directory, including through symlinks; the CLI refuses to overwrite the source deck.

• There is no cloud service, publishing endpoint, or telemetry.

Read SECURITY.md for the full threat model and the private vulnerability-reporting process.

Limitations

• Static, fixed-size slides only. v1 has no responsive layout mode, slide masters, themes, animation timeline, or transitions beyond none/fade/slide.

• No PPTX import or export, no video rendering, and no real-time collaboration.

• Scripts other than the presentation runtime are preserved but not executed by the editor or renderer; do not build layout with JavaScript.

• Tables support rows, columns, header toggling, cell fill, and borders, but not merging or splitting cells. Structural table edits reject merged cells.

• A document with no detectable slides is edited as one body slide; slide operations such as add, duplicate, delete, and reorder are unavailable in that fallback.

• PDF/PNG export depends on a locally installed Chromium-based browser.

• The project is local-only and pre-1.0. There is no upload, sync, or public publishing service.

Development

Prerequisites: Node.js 20 or newer, Git, and a Chrome/Edge/Chromium build for PDF/PNG export. Playwright Chromium is needed for E2E tests.

npm ci
npx playwright install chromium   # once, for E2E
npm run build
npm run verify:fast               # lint, dependency boundaries, types, unit, integration, matrix
npm run verify                    # everything, including E2E and package smoke

See CONTRIBUTING.md for the worktree, TDD, and local merge workflow, and docs/architecture.md for package responsibilities and data flow.

Documentation

• docs/contract.md - complete htmldeck/v1 contract.

• docs/mcp.md - MCP modes, tools, resources, errors, transcripts.

• docs/architecture.md - packages, data flow, revisions, preview commits, presenter protocol, renderer pipeline, tests.

• docs/testing.md - test strategy and feature-matrix rules.

• skills/htmlppt/SKILL.md - agent-facing skill.

License

MIT. See LICENSE.