The short version
- CBZ = ZIP. The most compatible option and the easiest to read in a browser.
- CBR = RAR. Often slightly smaller, but requires a RAR decoder with a restrictive licence.
- CB7 = 7z. Good compression, less common for comics, and frequently uses solid blocks.
Why CBR is harder in a browser
ZIP stores each file separately, and its directory sits at the end of the archive. A reader can jump straight to page 180. RAR supports solid compression, where many files are compressed as one stream. To reach page 180 in a solid archive, a decoder has to decompress everything before it.
The decoder is also a licensing question. UnRAR is free to use for extraction but is not an OSI-approved open-source licence, and it forbids using the code to build a RAR compressor. That is manageable for a reader, but it needs care in a commercial product.
What this reader supports
This version reads CBZ and ZIP. CBR and CB7 are not supported yet. The plan is to add them through a lazily loaded libarchive module, with a clear progress indicator for solid archives, rather than pretending a solid RAR can open instantly.
If you have a CBR and need to read it here today, convert it to CBZ with a local tool first. Do not upload a copyrighted comic to a random converter.
Which format should you keep?
For a personal library, CBZ is the safest default. It opens in more apps, on more devices, and in the browser without a native decoder. Use CBR or CB7 when the source only exists in that format, not as a deliberate archival choice.