What do you paste into a formatter that you'd never want uploaded?

I built PasteKit because I kept pasting API responses, JWTs and customer exports into online formatters, then wondering where that data went.

PasteKit formats and converts everything locally in your browser. Nothing is uploaded, and it works offline after your first visit.

I'm curious: what's the most sensitive thing you've pasted into an online tool? And what would make you trust a formatter with it?