Checking a book for Kindle¶

ValidationProfile::kindle() adds checks for sending a book to a Kindle (Send to Kindle) or publishing it with Amazon KDP. Pass it to validate(): the issues follow the structural ones, are ordinary ValidationIssue objects, and have a KINDLE_ code and a fix hint.

use PhpEpub\EpubFile;
use PhpEpub\ValidationProfile;

$epubFile = EpubFile::open('/path/to/book.epub');

foreach ($epubFile->validate(ValidationProfile::kindle()) as $issue) {
    echo $issue, "\n";
    if ($issue->fix !== null) {
        echo '  Fix: ', $issue->fix, "\n";
    }
}

PhpEpub\Kindle\KindleChecker does the checks: (new KindleChecker($epubFile))->check() returns only the Kindle issues. Amazon's documentation changes and is not a specification: treat this as a pre-flight check and use Kindle Previewer as the reference.

Rules and sources¶

A rule is sourced when a figure or requirement comes from an Amazon page; a heuristic rule could not be tied to an Amazon page and is always a warning. The URL of each source is in a comment next to the rule in src/Kindle/KindleChecker.php.

Code	Severity	Rule	Source
`KINDLE_FILE_TOO_LARGE`	error	The packaged book is above 200 MB, the web upload limit	Send to Kindle
`KINDLE_FILE_TOO_LARGE_FOR_EMAIL`	warning	Above 50 MB, the limit for sending by email	Send to Kindle by email
`KINDLE_COVER_TYPE`	warning	The cover is not a JPEG, PNG or GIF (e.g. WebP or SVG). KDP's JPEG/TIFF rule is for its cover upload, so the in-book formats are not held to it	KDP cover guidelines
`KINDLE_COVER_TOO_LARGE`	warning	The cover is above 10,000 pixels in height or width, or 50 MB or more	KDP cover guidelines
`KINDLE_NOT_UTF8`	warning	A content document is UTF-16, declares another encoding or is not valid UTF-8	Kindle Publishing Guidelines (characters should be UTF-8)
`KINDLE_UNSUPPORTED_SPACE`	warning	A content document uses a space other than the space, no-break space and zero-width non-joiner (e.g. the thin space or the ideographic space)	Kindle Publishing Guidelines, kindleformat
`KINDLE_COVER_TOO_SMALL`	warning	The cover's shortest side is under 500 pixels. KDP's own minimum (625 x 1,000) and its 1.6:1 ratio are for the cover it takes as an upload, so they are not checked	heuristic
`KINDLE_COVER_MISSING`	warning	The book declares no cover	heuristic
`KINDLE_AUTHOR_MISSING`	warning	The book has no `dc:creator`	heuristic
`KINDLE_FIXED_LAYOUT`	warning	`rendition:layout` is `pre-paginated`; KDP accepts fixed-layout EPUB, but no Send to Kindle page says how it is handled	heuristic
`KINDLE_SCRIPTED`	warning	A content document contains a `<script>`	heuristic
`KINDLE_DRM`	warning	The book is DRM-protected; no page says whether Send to Kindle takes it	heuristic

The cover rules are those of the cover image uploaded to KDP, which is not always the cover inside the EPUB, so they are warnings. The size is that of the book's files packed into a scratch archive that is removed again (skipped when the files are far below the limits); nothing in the book changes (unsaved package edits, a few hundred bytes, are not counted). Encrypted content is not read. Only the Send to Kindle size limits and the cover figures were checked against Amazon search results and the KDP cover page; the UTF-8 and space rules come from search summaries of the guidelines, which could not be fetched in full.