Reduce CBZ file size
Drop in a CBZ or ZIP and it re-encodes every page inside at the size and quality you pick, then hands the archive back. Large scans usually lose most of their weight with no visible difference on a phone screen.
- Runs on your device
- No upload, no server
- No account, no sign-up
CBZ/ZIP Reducer
Compress or Merge CBZ and ZIP archives. Images are optimized to reduce file size.
Upload ZIP, CBZ or Images
Drag & drop your files here
Reduction Settings
Images are re-encoded to shrink them, which is lossy — keep your original if you need it. Everything runs in this browser tab; no file is uploaded.
Why comic archives get so big
A CBZ is just a ZIP full of page images. Scans are often stored at print resolution — 3000px wide or more — which is far beyond what any phone or tablet can display. Re-encoding those pages to the resolution you actually read at is usually where the savings come from, not the archive format.
What the settings do
Shortest-dimension resolution caps the smaller side of each page, so tall pages and spreads scale consistently. Quality controls the encoder. Grayscale drops colour channels entirely, which helps a lot on black-and-white manga and nothing at all on colour comics.
Nothing leaves your device
The archive is opened, re-encoded and rebuilt inside your browser using WebAssembly. There is no upload step, no queue and no server that ever sees the file — which also means it works on files you would not want to hand to a web service.
Questions
Will this ruin the image quality?
Only if you tell it to. The default settings target the resolution a phone or tablet actually renders at, which is well below what most scans are stored at, so the visible result is usually identical. If you archive at print quality, raise the resolution cap or leave the file alone.
Does it work on CBR or RAR files?
No — CBR is a RAR archive, and RAR cannot be opened in the browser for licensing reasons. Convert to CBZ first, or use the BiblioFuse app, which reads CBR directly.
Is there a file size limit?
The limit is your device's memory, not a server quota, because the work happens locally. Very large volumes are fine on a desktop; a phone with several hundred megabytes of pages may run out of room.
BiblioFuse reads CBZ, CBR, EPUB, PDF and TXT on iPhone, iPad, Mac, Android and Windows — and streams big libraries straight from your own machine.
See BiblioFuse Reader