Apparently CodePen 2.0 sends data to their servers as you type

They send all typed into editor input to codepen.dev almost immediately (you would see in 1-2 sec after you typed your secret that it appears in respective Network/Response tab) even before one saved it. I tested this with a unique marker: after typing it into index.html, CodePen ran a build with "save:false", and the marker then appeared verbatim in the HTML served from the generated "*.codepen.dev preview". Thus, if you ever entered some secrets in there by mistake consider them compromized even if you did not publish/save the pen

Sent to them to render the preview pane. Same as pasting secrets anywhere on a browser.

Wait until you find out copying content on a computer might sent it over Wi-Fi/Bluetooth for sharing on other devices.

i made my own html playground that is browser only and shares preview via url hash because of these useless shenanigans of codepen, its not as featureful but i mostly use it for sharing single page html files

https://easyanalytica.com/tools/html-playground/

HotJar and similar services are (were?) popular as well, and those record your mouse pointer movements and clicks as well, then displays that as an overlay over the application, so it's essentially a "screen recording" of your session of the application.

There’s a detailed discussion of the same issue here https://www.reddit.com/r/webdev/comments/1rj1oac/i_planted_f...