What CBR to CBZ can read, and what it cannot write
CBZ is easier to open because it is a ZIP of the page images.
The comic pages are repacked from the RAR-based CBR into a CBZ.
Kindle files and DRM
A damaged RAR will fail. The pages are copied, not redrawn.
CBR to CBZ without the extra promises
CBR to CBZ sits on this site because CBR and CBZ are not interchangeable, even when they look similar in a file list. CBZ is easier to open because it is a ZIP of the page images. People convert CBR to CBZ so a reader that has no RAR support can open the comic. CBZ is the practical comic copy because ZIP is widely readable.
The comic pages are repacked from the RAR-based CBR into a CBZ.
Read this about CBR before you upload
CBR is a comic stored in a RAR archive. Browsers can read many RAR files and cannot create a new RAR. Creating a new CBR needs WinRAR. This site will not pretend to write one.
Keep the CBR until the CBZ opens.
Read this about CBZ before you send the download
The download has to be CBZ, because that is the format the next step named. CBZ is the practical comic copy because ZIP is widely readable. Page images can be packed and unpacked in the browser.
A CBZ with no images is rejected. Check the page order after you open it.
Keep, check, then delete
People lose time when they convert before they know which rule failed. Size, pixel dimensions, codec, font encoding, and layout are different rules. CBR to CBZ only addresses the CBR to CBZ step. CBZ is easier to open because it is a ZIP of the page images. The comic pages are repacked from the RAR-based CBR into a CBZ. A damaged RAR will fail. The pages are copied, not redrawn. The file stays in your browser and is not uploaded. The limit is 100 MB. Keep the original until the download has been opened in the program that will use it. Do the test with a short or simple file first when the real file is large. A one-page PDF, a single photo, or a one-minute clip will show you whether the output is the kind of file you needed. After that test looks right, run the real file once. Keep both the CBR original and the CBZ download until the receiving person or the upload form accepts it. Convert only a book you own and are allowed to convert. CBR to CBZ moves chapter text. A fixed illustrated layout is simplified, and DRM-locked files fail. Kindle formats can often be read here and not written. Keep the original ebook until the new file opens in the reader you actually use.
Here is the decision for CBR to CBZ. You start with CBR and you stop when a real program accepts CBZ. Unpacking to CBZ is the direction that works here. There is no upscaling of the art. You get the pictures that were in the archive. If those two sentences describe a tradeoff you do not want, do not convert. Renaming the extension by hand will not do this job. Running the tool twice on its own output will not do it either.
A damaged RAR will fail. The pages are copied, not redrawn.
A related step, if you still need one, is CBZ to CBR.
Other jobs start from the homepage, where each tool is named for the conversion it actually does.