I monitored the network traffic of popular free dev tools. Some of them contact 96 external domains when you paste code.

How to Test Webhooks Without Deploying: A Practical Guide

Your Code Is Not Private: I Audited What CodePen, JSFiddle, CodeSandbox, and Replit Do With Your Code

I Tested What Happens When You Upload Files to Free Online Converters — Your Documents Are Not Private