Convert EPUB3 to YML

Why Convert EPUB3 to YML?

Converting EPUB3 e-books to YML format is ideal when you need structured book data in the .yml file extension format used by many popular development tools. YML is functionally identical to YAML but uses the shorter extension preferred by Docker Compose, GitHub Actions, Symfony, and other platforms.

The .yml extension is the default choice for many DevOps and CI/CD tools. If you are building automated publishing pipelines with GitHub Actions, containerizing book processing with Docker Compose, or configuring Symfony-based content management systems, the .yml extension ensures seamless integration without file extension mapping.

This conversion produces the same clean, human-readable YAML content as the .yaml conversion but with the .yml extension. The choice between .yml and .yaml is purely a matter of convention -- some projects and tools prefer one over the other, and having both options available avoids compatibility friction.

The converter extracts EPUB3 metadata, chapter content, and navigation structure into a well-organized YML file with proper indentation, typed values, and multi-line string support. Comments can be added to annotate the data for collaborators working with the file.

Key Benefits of Converting EPUB3 to YML:

• Tool Compatibility: Many tools default to .yml extension (Docker, GitHub Actions)
• Human-Readable: Clean indentation-based syntax for easy editing
• DevOps Ready: Integrate book data into CI/CD and automation pipelines
• Comment Support: Annotate book data with inline comments
• Multi-Line Text: Store chapter content using block scalar notation
• Framework Integration: Works with Symfony, Spring Boot, and Rails configs
• Compact Extension: Shorter .yml is preferred in many project conventions

Practical Examples

Example 1: Book Metadata for CMS

Input EPUB3 file (cookbook.epub) — metadata:

<metadata xmlns:dc="http://purl.org/dc/elements/1.1/">
  <dc:title>Healthy Recipes</dc:title>
  <dc:creator>Chef Adams</dc:creator>
  <dc:language>en</dc:language>
  <dc:date>2024-08-10</dc:date>
  <dc:publisher>Kitchen Press</dc:publisher>
</metadata>

Output YML file (cookbook.yml):

# Book metadata extracted from EPUB3
book:
  title: "Healthy Recipes"
  creator: "Chef Adams"
  language: en
  date: 2024-08-10
  publisher: "Kitchen Press"

Example 2: Chapter Data for Static Site

Input EPUB3 file (tutorial.epub) — chapters:

<section epub:type="chapter">
  <h1>Introduction</h1>
  <p>Welcome to the tutorial. This guide
  will help you get started quickly.</p>
</section>
<section epub:type="chapter">
  <h1>First Steps</h1>
  <p>Begin by installing the software
  from the official website.</p>
</section>

Output YML file (tutorial.yml):

chapters:
  - title: "Introduction"
    order: 1
    content: |
      Welcome to the tutorial. This guide
      will help you get started quickly.
  - title: "First Steps"
    order: 2
    content: |
      Begin by installing the software
      from the official website.

Example 3: Navigation Structure

Input EPUB3 file (reference.epub) — TOC:

<nav epub:type="toc">
  <ol>
    <li><a href="part1.xhtml">Part I: Basics</a>
      <ol>
        <li><a href="ch01.xhtml">Chapter 1</a></li>
        <li><a href="ch02.xhtml">Chapter 2</a></li>
      </ol>
    </li>
  </ol>
</nav>

Output YML file (reference.yml):

toc:
  - label: "Part I: Basics"
    href: part1.xhtml
    order: 1
    children:
      - label: "Chapter 1"
        href: ch01.xhtml
        order: 1
      - label: "Chapter 2"
        href: ch02.xhtml
        order: 2

Frequently Asked Questions (FAQ)

Q: What is the difference between YML and YAML?

A: There is no difference in content or syntax. YML (.yml) and YAML (.yaml) are two file extensions for the same YAML format. The .yml extension is a shorter convention used by many tools (Docker Compose, GitHub Actions, Symfony), while .yaml is the extension recommended by the official YAML specification.

Q: Which tools prefer the .yml extension?

A: Docker Compose uses docker-compose.yml, GitHub Actions uses .yml files in .github/workflows/, Symfony uses .yml for configuration, Ruby on Rails uses database.yml, and many CI/CD tools default to .yml. The shorter extension has become a de facto standard in the DevOps and web framework ecosystems.

Q: Can I rename .yml to .yaml and vice versa?

A: Yes, you can freely rename between .yml and .yaml without any content changes. The files are parsed identically by all YAML libraries. The only consideration is that some tools look for specific extensions (e.g., Docker Compose specifically looks for docker-compose.yml).

Q: How is multi-line chapter content stored?

A: Chapter content uses YAML's literal block scalar notation (|) which preserves line breaks and indentation exactly as written. This makes the YML file readable even with long text passages. The > (folded scalar) can also be used when line breaks should be converted to spaces.

Q: Can I use this YML file with Docker Compose?

A: The book data YML file has a different structure than docker-compose.yml. However, you could create a Docker Compose configuration that mounts the book data file and processes it with a containerized application. The YML extension ensures Docker and related tools recognize the file format.

Q: Is the YML output safe to process?

A: Yes, the output contains only standard YAML data types (strings, numbers, dates, lists, maps). Always use safe YAML loaders (yaml.safe_load in Python, safeLoad in js-yaml) when parsing to prevent potential code execution from malicious YAML constructs. The converter never outputs unsafe YAML tags.

Q: How are EPUB3 dates formatted in YML?

A: Publication dates from EPUB3 metadata are stored as native YAML date values in ISO 8601 format (YYYY-MM-DD). YAML parsers automatically recognize these as date types, enabling proper date comparison and sorting in your application code without manual parsing.

Q: Can I include multiple EPUB3 books in one YML file?

A: Yes, YAML supports multiple documents in a single file using the --- separator. Each EPUB3 book can be converted to a separate YAML document within the same .yml file, making it convenient for managing book catalogs and collections in a single configuration file.