What this workbench inspects
The preflight validates the OCF ZIP entry map and CRC evidence, the exact root mimetype entry, META-INF/container.xml, package discovery, core metadata, manifest inventory, spine references, EPUB 3 navigation, EPUB 2 NCX linkage, duplicate IDs, resource media types, internal URLs, fragments, case-sensitive paths, and unlisted resources. The relationship view connects readable XHTML, SVG, CSS, and NCX references back to their package entries.
How safe repair works
The source is never overwritten. A corrected download is available only when every ZIP entry is readable and the proposed edits are deterministic. The rebuilt package puts the exact uncompressed mimetype entry first, rewrites only case-proven URLs, and corrects media types only where the selected bytes or well-known extension supply evidence. Rebuilt entries are stored without compression for a transparent, broadly readable result.
Important validation boundary
This is a bounded package preflight, not a complete EPUB conformance or accessibility certification. It does not execute scripts, decrypt content, fetch remote resources, validate CSS rendering, fonts, media overlays, accessibility semantics, digital-signature trust, schema vocabularies, reading-system behavior, or every version-specific EPUB rule. A signature file disables rebuilding because any change can invalidate its claims. Always run the output through the official EPUBCheck release and test it in the target reading systems.
Frequently asked questions
Why can one missing file create several messages?
A missing manifest resource can also break a spine item, navigation link, stylesheet link, or fragment target. Root-cause groups keep those relationships visible instead of hiding evidence.
Why is a media-type correction sometimes unavailable?
The tool corrects only formats it can identify conservatively from bytes or a well-known extension. It does not guess unfamiliar or vendor-specific content types.
Does a clean report mean the book is valid?
No. It means the package passed the checks implemented here. EPUBCheck, accessibility review, visual inspection, and testing in the intended reading systems remain necessary.
Can the corrected EPUB be smaller?
Usually not. Safe rebuilds store entries without compression. The goal is deterministic package repair and reviewability, not size optimization.
Authoritative references
The W3C EPUB 3.3 specification defines publication resources, package metadata, manifest, spine, navigation, and the OCF ZIP container. The W3C Publishing Community Group maintains EPUBCheck, the official EPUB conformance checker.
Browse publishing tools · Inspect an OpenDocument package · Inspect PDF page boxes