CBZ Comic Book Archive MIME Type

What does application/vnd.comicbook+zip mean?

The application/vnd.comicbook+zip media type identifies a CBZ comic book archive. A CBZ is a ZIP container whose members are comic pages, usually JPEG or PNG images, arranged for sequential reading. The registered extension is .cbz.¹

The +zip suffix tells software that the underlying representation follows ZIP rules. It does not mean that every ZIP file is a comic book. A CBZ reader still has to decide which archive members are pages and in which order to show them.

How can you identify a CBZ file?

The strongest practical clues are the .cbz extension, a valid ZIP structure, and a collection of page images. IANA deliberately lists no CBZ-specific magic number.¹ A non-empty ZIP commonly begins with the local-file-header bytes 50 4B 03 04, but those bytes identify the container, not its comic-book purpose. ZIP also permits other opening records, so checking only four bytes is not a complete validator.²

Renaming pages.zip to pages.cbz may be enough when the archive already contains correctly ordered images. Renaming an unrelated ZIP does not turn its contents into a readable comic.

Some libraries also put ComicInfo.xml in the archive. That community metadata file can describe the title, series, issue number, creators, publisher, language, page count, and page roles.³ It is useful but optional, and its presence is not part of the IANA media type registration.

Registration and format history

Comic readers used CBZ before it had an official media type. IANA registered application/vnd.comicbook+zip on July 1, 2016, with Kim Scarborough as the contact. The registration describes CBZ, together with CBR, as the de facto standard for comic book archives and names ComicRack, MComix, and Simple Comic as implementations.¹

The registration date is not the invention date of the filename convention. Because there is no published CBZ specification, the format has no standards document that establishes a single creator, version history, required image formats, filename sorting rule, or metadata vocabulary.

How to open a .cbz file

Use a comic reader or ebook application. calibre can import and convert comic archives, while IANA specifically lists MComix and Simple Comic among applications that use this media type.¹⁴ Ordinary web browsers do not provide a native CBZ reading mode, although a website or browser extension can implement one.

You can also inspect a trusted CBZ with a ZIP utility. That exposes the page images and any metadata files, but it loses reader features such as two-page spreads, right-to-left navigation, and remembered reading position.

Support in Poly

Poly recognizes both application/vnd.comicbook+zip and .cbz filenames. It classifies CBZ as a document, gives the original to calibre's ebook-convert, and stores the result as a PDF representation. The PDF pipeline then renders pages, extracts text, applies OCR fallback, and creates page-level embeddings.

After a successful conversion, Poly provides:

• A thumbnail and a paginated preview in the PDF viewer.
• Search across extracted or OCR-recognized page text.
• Visual similarity search for individual converted pages.
• Page count and rendered-page metadata.
• Page text and images that the Poly agent can read together.

This is a converted view, not a native CBZ reader. Poly does not expose the ZIP directory, individual source images, or ComicInfo.xml as separate searchable records. Page appearance and ordering depend on calibre's interpretation of the archive. Poly's document pipeline accepts files up to 1 GiB and processes at most 1,024 converted pages.

CBZ compared with CBR, CB7, and EPUB

The comic-book archive extension normally indicates the compression container:

CBZ is structurally simple and ZIP tools are broadly available. CBR and CB7 use different archive codecs, so changing their extensions to .cbz does not convert them. Extract the contents and create a new ZIP archive instead.

EPUB also uses ZIP, but it has a published package model, manifest, spine, navigation rules, and a required mimetype entry. CBZ readers mainly infer a sequence from images. EPUB is better when a publication needs documented navigation, accessibility semantics, reflowable text, or richer reading-system behavior.

Converting a CBZ

Choose the destination around the job:

• PDF for fixed pages, printing, and broad document compatibility.
• EPUB when a target reader requires an ebook package, while remembering that image-only pages do not become reflowable text automatically.
• A directory of images for editing, restoration, or OCR outside a reader.
• Another comic archive only when a particular device requires its container.

calibre's ebook-convert command selects the output format from the destination extension:⁴

ebook-convert comic.cbz comic.pdf
ebook-convert comic.cbz comic.epub

Check page order, double-page spreads, image dimensions, color, and metadata after conversion. OCR can make speech and captions searchable, but recognition errors are common with stylized lettering, curved balloons, vertical text, and low-resolution scans.

Security and privacy

A CBZ combines the risks of a ZIP archive with those of every embedded image decoder. IANA tells readers to validate the size and contents rigorously and applies the security considerations of both ZIP and the contained image formats.¹ Treat an unknown archive as untrusted even if its cover looks harmless.

Comic metadata may reveal more than the visible pages. ComicInfo.xml can include creator names, publication details, summaries, links, language, and reading-direction information.³ Review those fields before sharing a privately cataloged archive.

Is CBZ the same as ZIP?

CBZ uses ZIP as its container, but the labels communicate different intent. application/zip means a general archive. application/vnd.comicbook+zip means that the archive should be interpreted as sequential comic-book pages. A generic unzipper can extract a CBZ, while a comic reader adds ordering and reading controls.

Servers should send .cbz files as application/vnd.comicbook+zip. Falling back to application/zip preserves the container information but loses the more specific comic-book meaning.