EPUB to MOBI API

Turn an EPUB into a MOBI file for older Kindle devices and apps. calibre converts the book, chapters and images included.

How it converts

calibre converts EPUB to MOBI.

MOBI is the older Kindle format. For Kindles from the last decade, AZW3 keeps more of the book’s styling.
Books protected by DRM are refused before any work, and are not billed.

Should I use MOBI or AZW3?: AZW3 for any recent Kindle, since it keeps more styling. MOBI for older devices that cannot open AZW3.
Can it convert DRM-protected ebooks?: No. Books with DRM are refused before any work starts, and a refused file is not billed.

Price: 5 free conversions every month. Pro is $9 a month for 1,500, Scale $39 for 10,000. EPUB to MOBI costs the same as any other pair.
Largest file: 25 MB on Free, 100 MB on Pro, 250 MB on Scale.
Failed conversions: Never billed, and they don’t count toward your plan.
Your files: Deleted within 24 hours, along with the converted result.
How to call it: The REST API, described by an OpenAPI spec, or the MCP server from Claude or any other MCP client. Both use the same API key and quota.