Each tool has its own address and runs on the resume you drop or paste. Results stay in this browser; a count that a check ran is the only thing the server receives. “Fix these in the builder” opens the import review with the same resume.
Each answers one question: how a parser reads the resume, which keywords a posting wants, how well the resume matches it, and how the lines a posting asks for can be tailored with the facts kept. Each page says what it measures and nothing else.
For the text, yes: the same engine runs in both. The tools measure the uploaded file for the three document checks; the builder measures the page it renders, and both show the text-only subtotal so you can compare.
No. It works signed out and keeps everything in this browser. Once sign-in is switched on, an account is used only for a Pro pass, for applying to roles posted here, and for syncing your profile across devices.