HTML → MOBI/AZW3

What is HTML?

HTML / XHTML is the structural language of the web and is literally the content format inside an EPUB; .mhtml (MHTML) packs a page together with all its resources (images, CSS) into one file, which is what "save as a single page" produces. XML is the general markup language that formats such as FB2 and OPF are themselves written in. The whole family is tagged text where the tags carry the structure, so how much structure survives a conversion depends on how well the tool understands them.

What is MOBI/AZW3?

Mobipocket (.mobi) was long the default format Amazon accepted for Kindle delivery. AZW3 (also called KF8) is its successor with fuller HTML5/CSS support, and .azw is an earlier Amazon container. All three reflow and carry navigation and metadata, so they behave as one family. They are proprietary to Amazon's ecosystem, and since 2022 Amazon sends KFX/EPUB instead, so .mobi is mostly a legacy format now.

What to watch out for when converting HTML to MOBI/AZW3

Extracting from the source

All structure lives in the tags, but real pages mix in navigation, ads and footers that a naive conversion carries along. Extract the content container first (a readability pass), and note that <img> usually points outside the file — images must be downloaded and embedded before producing a single-file format.

Writing the target format

Producing .mobi/.azw3 requires Amazon's toolchain or Calibre. AZW3 supports reasonable CSS while legacy .mobi supports very little; for newer devices, target AZW3 — or simply deliver an EPUB.

Where the two formats interact

• Chapter headings in the source are ordinary lines while the target demands a real table of contents. Converters try to match patterns such as "Chapter N"; when the match is poor the TOC is garbled or the book has a single chapter. Check that TOC entries match the actual chapter count.

Post-conversion checklist

1. Convert the first three chapters as a trial and check for lost text, interleaved lines or misplaced blocks before doing the whole book.
2. Check chapter splitting: the TOC entry count should match the real chapter count.
3. Jump to five random spots and search a character name to confirm the text is fully searchable.
4. Confirm illustration count and placement — check that images are not all dumped at the end of a chapter.
5. Fill in title, author and language — a wrong language tag breaks typesetting such as Chinese line breaking.

Converting novels: what is different

Fiction is the most common and the most peculiar kind of e-book: hundreds or thousands of chapters, almost no figures, often nothing but a TXT source, and Chinese sources that frequently carry anti-piracy garbling. These are the points that bite hardest.

• A long novel can run to hundreds or thousands of chapters, so the table of contents decides whether the result is usable. Normalise chapter headings to one recognisable pattern first — say "Chapter N Title" alone on its own line — or the target will miss chapters, merge them, or collapse the whole book into one.
• Volume markers ("Volume One", "Volume Two") usually degrade to ordinary headings, losing the volume/chapter hierarchy. If that matters, promote volume headings one level in an editor afterwards so they are not siblings of chapter titles.

Tools for converting HTML to MOBI/AZW3

Any of the tools below can handle this direction; pick one by your operating system and how many files you have. Read the previous section first — doing the steps out of order (converting a scanned file before running OCR, for instance) usually means starting over.

Common questions

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