What TAR to ZIP does with the archive
A Linux server sent a TAR bundle, and a Windows user needs ZIP.
The TAR is unpacked in the browser and written as ZIP. TAR itself does not compress, so the ZIP may be smaller.
What still needs a desktop app
A .tar.gz or .tar.bz2 file belongs on the GZ or BZ2 page if this one cannot see the files inside. Open the ZIP and check the folder names.
TAR to ZIP without the extra promises
TAR to ZIP sits on this site because TAR and ZIP are not interchangeable, even when they look similar in a file list. A Linux server sent a TAR bundle, and a Windows user needs ZIP. A Windows user who received a TAR needs ZIP. A deploy script that asked for TAR needs the other direction. ZIP is the file you send when you do not know what the other computer has installed.
The TAR is unpacked in the browser and written as ZIP. TAR itself does not compress, so the ZIP may be smaller.
Read this about TAR before you upload
TAR bundles files without compressing them. Linux tools and many servers expect it. TAR itself does not compress, so the file can grow. A .tar.gz may need the gzip tool first if the files are still hidden.
Keep the archive the server gave you until the deploy or the unzip succeeds.
Read this about ZIP before you send the download
The download has to be ZIP, because that is the format the next step named. ZIP is the file you send when you do not know what the other computer has installed. RAR, 7Z, TAR, gzip, and bzip2 can be unpacked into ZIP here.
Open the ZIP and look at the file list before you delete the original.
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. TAR to ZIP only addresses the TAR to ZIP step. A Linux server sent a TAR bundle, and a Windows user needs ZIP. The TAR is unpacked in the browser and written as ZIP. TAR itself does not compress, so the ZIP may be smaller. A .tar.gz or .tar.bz2 file belongs on the GZ or BZ2 page if this one cannot see the files inside. Open the ZIP and check the folder names. 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 TAR original and the ZIP download until the receiving person or the upload form accepts it. Open the archive TAR to ZIP gives you before you delete the one you started with. Password-protected files fail. Some Unix downloads hide a TAR inside gzip or bzip2, so one conversion may not be the last step. ZIP is the file you can hand to a phone or a Windows PC without an extra app. Creating RAR or 7Z still needs a desktop program.
Here is the decision for TAR to ZIP. You start with TAR and you stop when a real program accepts ZIP. A TAR can be unpacked to ZIP, and a ZIP can be bundled as TAR. A ZIP of a PDF is not a meaningful compression of that PDF. Password-protected archives fail. 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 .tar.gz or .tar.bz2 file belongs on the GZ or BZ2 page if this one cannot see the files inside. Open the ZIP and check the folder names.
A related step, if you still need one, is ZIP to TAR.
Other jobs start from the homepage, where each tool is named for the conversion it actually does.