HTMLZ vs MD
A detailed comparison of HTMLZ eBook and Markdown — file size, quality, compatibility, and which format to choose for your workflow.
HTMLZ eBook
eBooksHTMLZ is a zipped HTML ebook format used by Calibre as a lossless intermediate representation. It packages HTML content, CSS stylesheets, and images into a single ZIP archive, preserving full formatting fidelity during ebook conversion chains.
About HTMLZ filesMarkdown
Documents & TextMarkdown is a lightweight markup language that uses plain text formatting syntax. It is widely used in software development, technical documentation, and content management systems.
About MD filesStrengths Comparison
HTMLZ Strengths
- Simpler than EPUB.
- ZIP-of-HTML portability.
- Calibre-native.
MD Strengths
- Readable as plain text even before rendering — fits in version control beautifully.
- Dead-simple: 90% of needs covered in 10 minutes of learning.
- Converts trivially to HTML, PDF, EPUB, and DOCX via Pandoc.
- Every modern IDE, note-taking app, and developer tool renders it natively.
- Lightweight — a typical Markdown file is kilobytes, not megabytes.
Limitations
HTMLZ Limitations
- Niche — no reader support.
- Not a mainstream delivery format.
- Calibre-only.
MD Limitations
- No formal authoritative spec — CommonMark, GFM, and MultiMarkdown differ on edge cases.
- Tables and complex layouts are clunky; footnotes and math require extensions.
- Links to images stay external — no embedded media unless you base64-inline.
- Styling is limited to what HTML allows — custom branding requires CSS outside Markdown.
Technical Specifications
| Specification | HTMLZ | MD |
|---|---|---|
| MIME type | application/x-htmlz | text/markdown |
| Extension | .htmlz | — |
| Container | ZIP + HTML | — |
| Tool | Calibre | — |
| Extensions | — | .md, .markdown, .mdown, .mkd |
| Standard | — | CommonMark, GitHub Flavored Markdown (GFM) |
| Encoding | — | UTF-8 (conventional) |
| Companion spec | — | RFC 7763 (2016) |
Typical File Sizes
HTMLZ
- Typical novel 300 KB - 2 MB
MD
- README 1-15 KB
- Blog post 2-30 KB
- Full technical manual 50 KB - 2 MB
Ready to convert?
Convert between HTMLZ and MD online, free, and without installing anything. Encrypted upload, automatic deletion after 2 hours.
Frequently Asked Questions
HTMLZ (HTMLZ eBook) is an ebook format designed for reading long-form text on dedicated e-readers, tablets, and ebook apps. It is part of the ebooks family and typically supports reflowable text, embedded images, chapter navigation, cover art, and metadata (title, author, ISBN) in a portable package.
Markdown is a lightweight text-based markup language created by John Gruber and Aaron Swartz in 2004. A .md file uses simple conventions (*italic*, **bold**, # headings, - lists) that compile to HTML. It became the default writing format for GitHub READMEs, Stack Overflow posts, Discord messages, and most developer documentation.
Dedicated e-readers — Kindle, Kobo, Nook, Pocketbook — support the most common ebook formats. On phones, Apple Books, Google Play Books, Moon+ Reader and KOReader all handle HTMLZ. For desktop reading, Calibre is the universal ebook viewer and library manager. Convert to EPUB or PDF for maximum compatibility.
Markdown files are plain text — open in any text editor. For formatted preview use VS Code (built-in preview), Typora, Obsidian, or upload to GitHub/GitLab which render Markdown automatically. Every note-taking app (Notion, Bear, Joplin) handles Markdown natively.
Upload your HTMLZ to KaijuConverter and pick EPUB, MOBI, PDF, AZW3, or similar targets. Our Calibre-powered pipeline preserves chapter structure, embedded images, cover art, and metadata. Conversion takes seconds for typical novels; long technical books with many images may take a little longer.
EPUB is the open ebook standard — it plays on every e-reader except older Kindles and in every major ebook app. PDF is better for fixed-layout content (textbooks, coffee-table books) and printing. Pick EPUB when the ebook is reflowable text, PDF when the layout matters more than the reading experience.