Show the Working

EPUB to HTMLZ

Nothing you choose here leaves your browser, and nothing is downloaded to make it work. Your browser already gzips and unzips; this page is the rest.

…or drop one anywhere on this page.

A book into the archive Calibre reads.

The chapters become one index.html, because an HTMLZ holds a single document where an EPUB holds several. The pictures come across as real files inside the archive, which is what Calibre expects, and a metadata.opf carries the title and author.

HTMLZ is Calibre's, and nothing else defines it

There is no published specification. An .htmlz is what Calibre writes: a ZIP with an index.html at its root, the pictures and stylesheets it refers to beside it, and usually a metadata.opf carrying the title and author. That is the whole of it.

So the only rule that matters is the name of that file. If an archive has no index.html but exactly one HTML file, this takes that one and says which it took. If it has several and no index, it refuses rather than guessing — picking the alphabetically first would be a coin toss with your book.

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