EPUB Checker
Check an .epub in your browser for structure, metadata, navigation, missing files, alt text, cover and accessibility problems.
Drop an EPUB file
or click to browseor tap to choose
Checked in your browser, nothing is uploaded
Large files (over 100 MB) may take longer or run out of browser memory
About EPUB Checker
Opens an .epub file in your browser and checks its structure and quality: the mimetype entry, container and package documents, metadata, table of contents, reading order, missing files, image alt text, the cover image, file size and accessibility metadata. Each check ends in pass, warning or fail with a plain explanation and a fix.
Drop an .epub file. The report appears straight away, with failures first. Read the fix line under each item, repair the book in your editor, and check it again. Download or copy the report to share with whoever formats the book.
This is a practical pre-check, not the official EPUBCheck validator, and a pass here does not guarantee that a store will accept the file. Run EPUBCheck as well before you upload to a retailer.
- Is this the same as EPUBCheck?
- No. EPUBCheck is the official validator from the W3C and checks the full specification, including schemas for XHTML, CSS and SVG. This tool is a practical pre-check of structure and common quality problems. A file can pass here and still fail EPUBCheck or a store's review, so use EPUBCheck before you publish.
- Why does the mimetype file matter?
- The EPUB specification requires a file named mimetype containing exactly application/epub+zip, stored first in the archive without compression, so readers can recognize the format. Some readers and stores reject a file where it is compressed or not first. The tool reports which of these is wrong.
- What does a warning mean compared with a fail?
- A fail is something the specification requires or that stops content from showing, such as a missing file or a malformed page. A warning is a quality or accessibility issue that does not stop the book opening, such as a missing author, images without alt text or accessibility metadata that is not declared.
- Why is an empty alt attribute a warning?
- An alt attribute left empty tells screen readers to skip the image, which is right for ornaments but wrong for pictures that carry meaning. The tool cannot know which you meant, so it asks you to review them. Images with no alt attribute at all are counted separately.
- Is my book uploaded anywhere?
- No. The file is read in your browser tab and the report is built there. Nothing is sent to a server.
How to use EPUB Checker
Drop an .epub file on the page. The tool opens it as a ZIP in your browser and lists each check as pass, warning or fail, with failures first, a plain explanation and a fix line. The side panel shows the book overview and its reading order with chapter titles. Download or copy the report, repair the book in your editor and check it again.
When to use it
Use it before uploading an ebook to a store or sending it to a reader, to catch common problems quickly: a mimetype file that is not first or is compressed, a missing container or package document, missing title, language or identifier, files listed but absent, a table of contents that points nowhere, pages that are not well-formed XML, images without alt text, a small cover and absent accessibility metadata.
When not to use it
Do not treat it as a replacement for the official W3C EPUBCheck validator or a store's own review. It does not validate CSS, the full XHTML or SVG schemas, fonts, media overlays or fixed-layout rules. It cannot tell you whether a particular store will accept the file, and it does not repair the book.
Tips for best results
Fix the failures first, since a missing container or package document hides the checks that follow. Capitalization matters inside an EPUB, so a file listed as Cover.jpg will not match cover.jpg. After fixing, run the official EPUBCheck as well, because it covers areas this tool does not.
Limitations
The XML reader checks well-formedness (tags, quoting, entities) but not schemas. Alt text is judged by the alt attribute only, so an empty alt is reported as a warning because it marks an image as decorative. Cover size is measured for PNG, JPEG and GIF files. The size thresholds are rules of thumb, not store limits. Files over 100 MB are not accepted.
Privacy
The EPUB is opened and checked entirely in your browser with a ZIP reader. It is not uploaded, stored or logged, and it disappears when you close or reload the tab.
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