Are my files uploaded?

No. Files are read and processed inside your browser. They are never sent to a server, and closing the tab discards them.

Can I add a password?

Not to the ZIP itself. To protect files with a password, use the Encrypt File tool, which uses AES-256.

The archive is built in browser memory, so the practical limit depends on your device. A few hundred megabytes works on most computers.

JavaScript is turned off. InspireTools processes files in your browser, so the tools need JavaScript to run.

Bundle files into a ZIP, TAR or TAR.GZ archive, with your choice of compression.