Open DevTools (F12), click Network, clear it, then paste your config. The Network tab stays empty. No requests are made — your config never leaves this browser.
Turn off your WiFi after this page loads. The tool keeps working. That's the proof — everything runs as JavaScript in your browser, not on a server.
In DevTools console, run this and see an empty result:
Object.keys(localStorage)
Nothing is saved. Close the tab and your config is gone forever.
The entire tool is one HTML file you can view. Right-click → View Source. The redaction logic is right there in plain JavaScript. Audit it yourself.