Convert OPF to MOBI

Older Kindle software and some ebook workflows still request a .mobi file, while an OPF file is usually only the package manifest inside an EPUB project. The conversion therefore requires the complete EPUB source, not the OPF XML alone.

What the OPF format is

OPF is an XML package document used by EPUB. It stores metadata, lists the book’s XHTML, images, stylesheets, fonts, and navigation files in a <manifest>, and defines their reading order in a <spine>. The OPF normally contains neither the book’s text nor its images.

EPUB authoring tools such as Sigil, calibre Editor, Adobe InDesign, and publishing systems create an OPF inside an EPUB package. You may encounter one after extracting an EPUB archive, editing ebook source files, or receiving an unfinished publishing project. Its referenced files and relative directory paths must remain available for conversion.

What the MOBI format is

MOBI is a reflowable ebook format associated with older Amazon Kindle software and devices. It combines ebook content, metadata, and navigation in one file and supports adjustable text size, chapters, hyperlinks, basic images, and common ebook metadata.

MOBI is useful when a legacy Kindle or application specifically requires .mobi. Its CSS, typography, layout, SVG, table, and font support is more limited than modern EPUB, and current Amazon publishing workflows generally use EPUB or Kindle Create/KPF output instead. MOBI does not provide Amazon DRM.

Convert the source with calibre

1. Install the desktop version of calibre from calibre-ebook.com.
2. Keep the OPF with every file referenced by its <manifest>, preserving each file’s relative path. This normally includes XHTML or HTML files, images, CSS, fonts, the EPUB 2 NCX file, or the EPUB 3 navigation document.
3. In calibre, select Add books and add the OPF if your version accepts it. Select the imported book and choose Convert books.
4. Choose MOBI as the output format. Check the title, author, language, and cover in Metadata; use Structure detection only when the source lacks reliable chapter structure.
5. Start the conversion and use Open containing folder to locate the generated file.

The command-line equivalent is:

ebook-convert book.opf book.mobi --output-profile kindle

Replace the filenames with actual paths. The kindle output profile applies Kindle-oriented formatting; omit it when the target software does not need that profile.

Build an EPUB when the OPF is rejected

An OPF cannot be converted independently when its resources are missing, its paths are broken, or it is not a valid EPUB package document. Reconstruct the EPUB directory structure, usually with the OPF under OEBPS/, and add:

• mimetype at the archive root, containing exactly application/epub+zip;
• META-INF/container.xml, pointing to the OPF, for example <rootfile full-path="OEBPS/content.opf" media-type="application/oebps-package+xml"/>;
• every XHTML, image, stylesheet, font, and navigation resource named by the OPF.

When creating the ZIP archive, make mimetype the first entry and store it without compression. Rename the archive to .epub, validate it, then convert it with:

ebook-convert book.epub book.mobi

Use EPUBCheck to identify invalid XML, missing manifest resources, broken links, and packaging errors before conversion. If the OPF came from an extracted EPUB, recreating the original package is safer than moving files into a new layout.

Use an online converter

Online services generally support EPUB-to-MOBI, not standalone OPF-to-MOBI conversion. After creating a valid EPUB, services such as CloudConvert or Convertio can be used if their current format lists show EPUB as the input and MOBI as the output. Upload only material permitted by the service’s retention and privacy terms; source files may contain unpublished or copyrighted content.

Check the converted file

Conversion cannot restore files absent from the OPF manifest or repair incorrect relative paths. Open the MOBI in calibre’s viewer and test it on the intended Kindle or legacy application; inspect the table of contents, cover, chapter breaks, links, images, and metadata.

Complex CSS, fixed-position layouts, SVG, embedded fonts, tables, footnotes, right-to-left text, media overlays, JavaScript, and interactive elements may be simplified or lost. Keep the EPUB as the master copy. For current Kindle delivery, test the EPUB in Kindle Previewer and use the format produced by Amazon’s supported publishing workflow rather than generating MOBI unless a legacy target explicitly requires it.