HTMLZ to EPUB Converter

Convert HTMLZ to EPUB online for free. Fast, secure, and high-quality conversion with no sign-up or software required.

Free to useNo file stored beyond 1 hourEncrypted over TLS 1.2/1.3No watermarks

or drag and drop files here

Maximum file size is 1GB

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How it works

Three steps to your converted file

Everything happens in your browser tab - upload, pick a format, download. The heavy lifting runs on our servers.

Upload your file

Drag and drop, click to browse, or paste a URL. Batches take up to 20 files at once - 230+ input formats across video, audio, image, document, and archive types.

Choose an output format

Pick from over a hundred output formats. Filter by category or search by name - every option is open to everyone, no account needed.

Convert & download

Hit Convert and grab your download link moments later. Originals are erased when the job completes; results are cleared within about an hour.

What is an HTMLZ file?

HTMLZ is a zipped container format created primarily for the Calibre eBook management software to package HTML content into a portable eBook structure. It comprises a ZIP archive holding an index.html file, a style.css stylesheet, image assets, and a metadata.opf file following the Open Packaging Format standard. Unlike EPUB, HTMLZ does not enforce the strict containment structure of the IDPF specifications, serving instead as a lightweight wrapper for HTML-based text.

How to open an HTMLZ file

HTMLZ files are natively processed by the Calibre e-book management suite, which can view or convert them to standard formats like EPUB or MOBI. Because the underlying structure is a ZIP archive, users can also rename the file extension to .zip and extract the HTML and CSS components using standard compression utilities like 7-Zip or WinRAR for manual viewing in a web browser.

HTMLZ Technical Info

Full Name: Zipped HTML eBook
Developed By: Kovid Goyal (Calibre)
Initial Release: 2010s
MIME Type: application/zip

What is an EPUB file?

EPUB (Electronic Publication) is an open e-book standard maintained by the World Wide Web Consortium (W3C), originally developed by the International Digital Publishing Forum (IDPF). It utilizes the Open Container Format (OCF) based on ZIP compression to package XHTML content, CSS styling, and XML metadata. EPUB supports reflowable content, allowing text to adapt to various screen sizes, and fixed-layout rendering for graphic-heavy publications. The current version, EPUB 3.2, supports HTML5, SVG, and JavaScript interactivity.

How to open an EPUB file

EPUB files require dedicated e-reader software as most operating systems do not natively render them. On desktop environments (Windows/macOS/Linux), Calibre is the industry-standard management tool, while Adobe Digital Editions handles DRM-protected files. For mobile devices, Apple Books (iOS) and Google Play Books (Android) provide native rendering. Browser-based extensions like EPUBReader for Chrome allow viewing without standalone software.

EPUB Technical Info

Full Name: Electronic Publication
Developed By: IDPF / W3C
Initial Release: 2007
MIME Type: application/epub+zip

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Why RunConvert

The fastest way to convert any file

Purpose-built for speed, privacy, and breadth of format support.

Convert HTMLZ to EPUB in seconds

Every HTMLZ to EPUB conversion runs on our servers, so your device stays fast and the output quality stays intact.

Fast, cloud-powered

No queue, no waiting. Files are processed on high-performance servers and returned in seconds, even for large files.

Secure & private

Encrypted in transit and never shared with anyone. Uploads are erased the moment your job completes, and results shortly after.

Free - no account needed

Convert without creating an account - no credit card, no trial clock. Sign in only if you want history and higher daily limits.

Developer API

Convert HTMLZ to EPUB via API

Automate HTMLZ to EPUB conversions in three steps: create a job, upload your file, then poll for the result.

# 1. Create job
curl -X POST https://api.runconvert.com/v3/jobs \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "tag": "htmlz-to-epub",
    "tasks": {
      "upload-file": {
        "operation": "import/upload"
      },
      "convert": {
        "operation": "convert",
        "input": "upload-file",
        "output_format": "epub"
      },
      "export-result": {
        "operation": "export/url",
        "input": "convert"
      }
    }
  }'

# 2. Upload your file (use upload_url from the response)
curl -X PUT "$UPLOAD_URL" --upload-file input.htmlz

# 3. Poll for result
curl https://api.runconvert.com/v3/jobs/$JOB_ID?include=tasks \
  -H "Authorization: Bearer YOUR_API_KEY"

Replace YOUR_API_KEY with your RunConvert API key. Get your free API key at runconvert.com/api.