How to Fix the EPUB Mimetype Error (Offset 30 STORE & container.xml Guide)

Why zipping an EPUB folder in Finder or Explorer breaks the book

An EPUB file uses the ZIP container format, so renaming .epub to .zip and extracting the archive is a normal way to inspect stylesheets, fonts or chapter XHTML files. The problem starts when you re-compress the folder with a general-purpose desktop archiver such as macOS Finder ("Compress") or Windows File Explorer ("Send to Compressed folder").

An Open Container Format (OCF) publication is not an arbitrary ZIP archive. Under the W3C EPUB 3.3 OCF ZIP Container specification, a valid EPUB must place a file named mimetype as the very first entry in the archive, store it uncompressed (STORE, compression method 0), omit any local ZIP extra fields on that first header, and write the exact 20-byte ASCII string application/epub+zip starting at byte offset 38 (immediately after the 30-byte local file header and the 8-byte filename mimetype).

Diagnose the archive in your browser before repacking

Before running command-line flags or re-exporting a manuscript, test the broken file in the interactive EPUB Preflight Checker or the inspector embedded at the end of this guide. The browser-only inspector reads the local ZIP central directory and byte offsets 0..58 without uploading your book, showing immediately whether mimetype was deflated, shifted by a ZIP extra field, or buried inside a subfolder.

If your source book is still in an older Kindle format or another ebook container, use the Ebook Format Selector to check which format your target device requires, or convert a DRM-free source directly with the MOBI to EPUB converter so the browser builds the OCF container in the required order.

Fix 1: Repack the EPUB with zip -0 -X so mimetype sits at offset 30

When repackaging an extracted EPUB folder from the command line, always run zip from inside the directory that directly contains mimetype, META-INF/ and OEBPS/ (never from the parent directory outside it). Create the archive in two steps:

1. Write mimetype first with zero compression and no extra fields: run zip -0 -X ../repaired-book.epub mimetype. Flag -0 forces STORE (compression method 0), and -X strips operating-system extra fields so the filename begins at byte offset 30 and the 20-byte application/epub+zip payload begins at byte offset 38.
2. Append META-INF/ and the content directory recursively: run zip -r -9 -X ../repaired-book.epub META-INF OEBPS -x "*.DS_Store" "__MACOSX/*". Those remaining entries can use standard DEFLATE compression without disturbing the first header.

Verify that the mimetype file itself contains exactly 20 bytes with no trailing newline. If a text editor appended a line break, rewrite it without a newline before running the first zip command.

Fix 2: Remove parent folder wrappers and check META-INF/container.xml

A second common failure happens when a user compresses the outer folder my-book/ instead of its contents. That produces archive paths like my-book/mimetype and my-book/META-INF/container.xml. Even if mimetype were uncompressed, its filename in the local header would be my-book/mimetype (16 bytes instead of 8), and no reading system will find META-INF/container.xml at the root of the archive.

Open META-INF/container.xml and confirm these three requirements:

• The file path inside the ZIP is META-INF/container.xml with uppercase META-INF and lowercase container.xml — ZIP entry paths in EPUB are case-sensitive.
• It contains a <rootfile full-path="..." media-type="application/oebps-package+xml"/> element whose full-path matches the exact case and directory of your .opf package document (such as OEBPS/content.opf or EPUB/package.opf).
• The referenced .opf file actually exists at that exact path in the ZIP archive and does not start with a leading slash.

Fix 3: Check OPF manifest, spine and NCX/nav consistency after container repair

Fixing the OCF container gets your EPUB past the initial signature check, but Amazon Send to Kindle and strict readers also inspect the OPF package document that META-INF/container.xml points to. Review our EPUB table of contents and character encoding repair guide if the book still fails after repacking.

In particular, verify that every file referenced in the OPF <manifest> is present in the ZIP archive with identical capitalization, every idref in the <spine> matches a manifest id, and at least one navigation document (properties="nav" in EPUB 3 or an NCX table of contents in EPUB 2) is declared.

Verify with the preflight inspector and EPUBCheck before delivery

Once your repackaged file is ready, run both a fast structural preflight and a full specification check before sending the book to a reader:

1. Drop the repaired .epub into the EPUB Preflight & Container Inspector below to confirm all six OCF container checks pass in your browser.
2. Run the official W3C EPUBCheck validator locally to verify XHTML markup, CSS rules and OPF metadata schemas beyond the OCF container header.
3. If your destination is an older Kindle over USB rather than Send to Kindle (see our Kindle EPUB and Send to Kindle guide), convert the validated EPUB using the EPUB to AZW3 converter or the legacy EPUB to MOBI converter.

• Original EPUB backup is saved before editing or repacking.
• Bytes 0..3 are 50 4B 03 04 and the archive is a real ZIP container.
• First ZIP entry is mimetype (8 bytes) at offset 30 with extra-field length 0.
• mimetype uses compression method 0 (STORE) and equals application/epub+zip (20 bytes, no newline).
• META-INF/container.xml exists at the archive root and points to an existing .opf package document.
• Repacked EPUB passes both the browser OCF preflight check and local EPUBCheck validation.

Check an EPUB’s packaging before you convert or send it

Scope: Basic OCF packaging preflight only — not official W3C EPUBCheck certification, DRM removal, or guaranteed Amazon Send-to-Kindle acceptance.

Readers reject an EPUB when its ZIP container is assembled in the wrong order. Try a sample package or check your own file — it is read locally in your browser and not uploaded.

Sample packages

Valid EPUB 3 PackageMissing mimetype First EntryDeflated mimetype (Compression=8 Error)Missing META-INF/container.xmlDRM / Encrypted Archive Notice

Check your own .epub fileOr drop it here. Up to 50 MB, read on this device only.

Packaging problem found Result for Deflated mimetype (Compression=8 Error). 1 packaging check failed.

Result for Deflated mimetype (Compression=8 Error)

1 packaging check failed. 1,258 bytes, 4 ZIP entries.

• Pass ZIP local file header signature (PK\x03\x04)
  Starts with 50 4B 03 04 (ZIP local file header).
• Pass First entry is “mimetype” at byte offset 30
  “mimetype” is the first entry (name at byte 30, payload at byte 38).
• Fail “mimetype” is stored uncompressed (method 0)
  Compression method 8 (DEFLATE). OCF requires “mimetype” to be stored uncompressed.
• Not checked “mimetype” payload is exactly application/epub+zip
  Not checked: compressed bytes are not readable as plain text without inflating.
• Pass META-INF/container.xml and an .opf package document exist
  Found META-INF/container.xml and OEBPS/content.opf.
• Pass No unsafe archive paths (../, absolute or drive paths)
  4 entries with relative paths.
• Pass No encryption or DRM markers
  No META-INF/encryption.xml or encrypted ZIP entries.

Next step

Open EPUB package checks & repairs →

• EPUB to AZW3 →
• EPUB to MOBI →
• Send to Kindle EPUB guide →