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EPUB to HTML

Nothing you choose here leaves your browser, and nothing is downloaded to make it work — not a library, not a reader, nothing. An EPUB is a ZIP of web pages, and your browser already knows how to deflate; this page writes the book around it.

…or drop one anywhere on this page.

One web page, with the pictures inside it.

A book is already a set of web pages — this joins them into one file in reading order. The pictures live inside the book's ZIP, so a link to them means nothing once the page is on its own; most converters leave the tags in place and let them break. These are read out and written into the file itself, so what you get is a single document that works anywhere with nothing beside it. That makes it bigger, and the figure is shown before you download it.

What an EPUB actually is

A ZIP file with a particular set of things in it. A mimetype file saying application/epub+zip, a META-INF/container.xml pointing at a package file, that package file listing everything the book contains and the order to read it in, and then the chapters, which are ordinary web pages. Rename an EPUB to .zip and you can open it with anything.

One rule in there catches nearly everybody who writes one by hand: the mimetype entry must be first in the archive and stored uncompressed, so that a reader can identify the file by reading twenty bytes at a fixed position without unzipping anything. Compress it and you have a perfectly valid ZIP that no e-reader will accept as a book. That was checked against a real book from Project Gutenberg before this was written, and it is checked again every time these pages are tested — by Python, which did not write them.

Books you bought are usually locked, and this says so

Most shops sell books wrapped in DRM. The chapters inside are encrypted, and nothing can read them without the key — not this page, not any converter, whatever it claims. The book announces this itself, in a file called META-INF/encryption.xml, so it is recognised and said plainly rather than producing a file full of unreadable characters and leaving you to wonder what you did wrong.

That is a limit of the file, not of the tool. A tool that appears to do it anyway is either stripping the protection, which is a legal question rather than a technical one, or giving you nonsense.

Why there is no EPUB to PDF here

Because it is not a conversion. A PDF fixes text to a page; an EPUB deliberately has no pages at all, and reflows to whatever it is read on — that is the entire point of the format. Going from one to the other means typesetting: choosing a page size, a typeface, a size, a margin, and where every break falls. Those are real decisions, and a converter that makes them silently has made them for you. An e-reader, Calibre, or a word processor will do it with the choices in front of you, which is the right place for them.

What it will not do

It will not lay the book out for you. What comes out is the book's own structure with a plain, readable stylesheet on top — not the publisher's design, which lives in stylesheets that are dropped because they assume a reader's own page. Footnote links that pointed between chapter files will not go anywhere once everything is one page.

It does not open MOBI, AZW or AZW3 — Amazon's formats, which are a different container entirely and, in the case of anything bought from the Kindle store, encrypted as well. It does not open password-protected ZIPs. And it is not a proofreader: what goes in is what comes out, tidied but not rewritten.

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