SEED.html - Simple EPUB EDitor

A modern browser-based EPUB editor that transforms plain text into beautifully formatted ebooks. Built with Svelte, TypeScript, and modern browser APIs.

Overview

SEED.html is a sophisticated EPUB editing application that runs entirely in your web browser. It enables authors to create, edit, and publish EPUB files using a simple plain text workflow with powerful transformation capabilities.

Key Features

• Plain Text to XHTML Transformation - Write in plain text, publish as valid, accessible EPUB 3
• Browser-Based - No installation required, works offline after first load, installable as a PWA
• Multi-Device Preview - See how your book looks on different devices, with different Reading System configurations
• Extensible Transform System - Customize text processing with JavaScript (for auto-generated glossary, index, list of figures)
• Accessibility-First Design - Full keyboard navigation and screen reader support
• Internationalization - Available in multiple languages with RTL support for writing
• Browser-based File Storage - Uses OPFS and IndexedDB for persistent local storage

Distribution

SEED.html is distributed under the terms of the MIT license. It is free to use, modify and distribute. In addition to the source repository it may be available in these ways;

1. Web Application - Access at readitinabook.com for immediate use
2. Downloadable HTML - Save locally from the above site for offline authoring by opening the SEED.html file from your device
3. Embedded in EPUBs - The core SEED.html app can be added to an EPUB as a non-manifest item, so it travels with the book for the life of that artifact
4. npm package - npx seed-html serves the full app (including the extensions and plugins catalogs the single file can't carry) on your own machine — see seed-html on npm

See USER_GUIDE.md for detailed usage instructions.

Alternatives

Why another EPUB tool? SEED.html is built for one job — authoring accessible EPUB 3 books in the browser from plain-text sources — rather than converting between many formats or laying out for print. Here is a quick comparison with other tools you might reach for. A ✅ marks a first-class strength, ⚠️ a capability that comes with caveats (see the note under the table), ❌ something deliberately out of scope, and a blank means it is simply not a goal of that tool. For the detailed, caveated version see COMPARISON.md.

	SEED.html	InDesign	Sigil	Calibre	Pandoc	Quarto	Vellum
Runs in a browser (including iOS and Android)	✅
Free & open source	✅		✅	✅	✅	✅
Plain-text, version-controlled chapter source	✅				✅	✅
Choose your markup (Markdown / Djot / Textile)	✅				✅
Purpose-built for EPUB (not a converter)	✅		✅
Live device & reflow preview	✅		✅	✅			✅
Built-in live accessibility & validation checks	✅
Edits existing third-party EPUBs	❌		✅	✅
Self-editing EPUBs	✅

⚠️ PDF export. SEED can generate a PDF straight from your plain-text source, but it renders through the browser's own print pipeline (a Paged.js polyfill) rather than a print-typesetting engine, so fine layout control is limited — treat it as a convenience output, not a rival to InDesign. On Chrome and Edge the result is a tagged PDF, a solid starting point for downstream accessibility treatment.

Technology Stack

• Frontend Framework: Svelte 5 with TypeScript
• Build System: Vite 6
• Local Storage: OPFS (Origin Private File System) with IndexedDB fallback
• EPUB Processing: Browser-native Compression Streams API
• Testing: Vitest with happy-dom
• Documentation: Storybook for component development

Development

This section is for developers maintaining or extending SEED.html.

Prerequisites

• Node.js 20+ (LTS recommended)
• npm 10+
• Modern browser (Chrome/Edge 119+, Firefox 119+, Safari 17+)

Setup

# Clone the repository
git clone https://github.com/stewarthaines/seed-html.git
cd seed-html

# Install dependencies
npm install

# Start development server
npm run dev

Agent assistance (dev server and npm installation only)

The repo includes an MCP bridge (scripts/agent-bridge.mjs) that connects a coding agent such as Claude Code to the running dev app, so the agent works against your live project: it can read source files and settings, follow the transform pipeline, inspect the rendered chapter as you see it, and — with your in-app approval, per write — edit chapter sources, stylesheets, and transform scripts. Useful when debugging CSS, transform output, or reading-system behavior. The bridge also serves an authoring guide (docs/AGENT_AUTHORING.md) that teaches the agent the project's EPUB and pipeline constraints before it may write.

# One-time: register the bridge with your agent CLI
claude mcp add seed-bridge -- node scripts/agent-bridge.mjs

Then: start npm run dev and open the app, start the agent session (the session spawns the bridge and keeps it alive), and click Allow agent assistance (robot icon, sidebar footer). The connection lasts for the session; every agent action appears in an in-app activity feed, and writes prompt for approval individually.

This is a local-workbench feature only: the button and module are absent from production builds. Design and security model: process/AGENT_BRIDGE.md.

Quality Standards

This project maintains zero TypeScript errors at all times. Before committing:

# Run all quality checks
npm run check && npm run lint && npm test

See DEVELOPMENT.md for comprehensive development guidelines.

Key Documentation

• CLAUDE.md - AI coding agent instructions
• DEVELOPMENT.md - Development workflows and standards
• TESTING.md - Testing strategy and patterns
• DEPLOYMENT.md - Build and deployment instructions
• LOCALIZATION.md - Adding new languages and translations
• COMPARISON.md - How SEED.html compares to other EPUB tools

Project Structure

seed-html/
├── src/
│   ├── lib/           # Core libraries with API documentation
│   ├── routes/        # Application views
│   ├── stores/        # Svelte stores
│   └── styles/        # Design system
├── static/            # Static assets (inlined at build)
└── stories/           # Storybook component demos

Building

# Production build
npm run build

# Preview production build
npm run preview

The build creates a single index.html file in the dist/ directory with all assets inlined.

License

(c) 2025 Stewart Haines

This software is open source under the terms of the MIT license. See LICENSE.txt for full terms.

Support

For bug reports and feature requests, please use github.