Canon Service Tool V5204 Portable -

Canon Service Tool v5204 Portable: A Technical Overview

But what exactly is this tool? Is it safe to use? And does a "portable" version exist?

Never reset ink levels without physically refilling the cartridge first.

No. The tool resets the ink level monitoring chip on some compatible cartridges, but it does not add physical ink. If you reset the chip on an empty cartridge, the printer will think it is full and run dry, destroying the print head. canon service tool v5204 portable

Ensure the "USB Port" field in the top right shows your printer. In the "Clear Ink Counter" section, find Canon Service Tool v5204 Portable: A Technical Overview