I almost leaked a customer's data while screen-sharing ChatGPT — here's what I built to stop it

A few weeks ago I was on a call sharing my screen, walking a teammate through a prompt I'd been iterating on in ChatGPT. Mid-sentence I scrolled up — and there, three messages back, was a chunk of a customer's data I'd pasted in earlier to debug something. Real email, real account info, sitting right there on a shared screen. Nobody said anything. Maybe nobody noticed. But I noticed, and I spent the rest of the call only half-present, trying to remember everything else still in that thread. If you live in ChatGPT all day, you already know the problem. The thread is your scratchpad. You paste logs, keys, customer rows, half-finished internal docs — things you'd never put in a doc you planned to share. And then someone says "can you share your screen real quick" and suddenly your scratchpad is a presentation. Why the usual advice doesn't work The standard answers are all some version of "be careful": Open a clean tab before sharing. Scroll to the top. Use a separate "demo" account. These fail for the same reason all manual checklists fail under pressure: the moment you actually need them is the moment you're distracted, talking, and not thinking about hygiene. You remember after . The fix has to happen before the screen goes live, and it has to require zero discipline in the moment. What I wanted instead I wanted something that just sat there and blurred sensitive parts of a page automatically, so that even if I forgot, the leak couldn't happen. A few requirements: Local only. Whatever it does, it never sends page content anywhere. A privacy tool that phones home is a contradiction. Before, not after. It blurs while the page renders, not after I've already exposed it. Per-element, not whole-screen. A full black box is useless for a demo. I still need to show the working parts. The interesting technical bit The naive approach is to listen for some "I'm sharing now" signal and react. That's too late — there's a visible frame where the data is exposed before the blur kic