Privacy

Code in the editor, saved snippets, saved inputs, whiteboard sketches, the theme, playback speed, layout and every other preference are written to your browser’s local storage. They are not uploaded, not backed up and not readable by us. Clearing your browser data deletes them, and nothing anywhere else changes.

Code you run is executed inside a sandboxed Web Worker on your own machine. It is never sent to a server to be run.

When a page has been open and actively used for ten seconds, thirty seconds, a minute and so on, the browser sends one short message recording that the mark was crossed. It carries the page’s name, the milestone, and two random identifiers — one that lives in local storage and one that dies with the tab — so that forty readings can be told apart from one person reloading forty times.

Those identifiers are random numbers generated on your device. They are not derived from anything about you, mean nothing anywhere else, and are stored only inside a counting structure that keeps a hash rather than the value. Nothing in it can be turned back into a person; it can only be counted.

Page views and performance timings are also collected in aggregate by Vercel Analytics and Vercel Speed Insights, which the site is hosted on.

The algorithm example pages carry advertising from Google AdSense. Google and its partners use cookies or similar identifiers to serve and measure those ads, and they receive your IP address, browser details and the address of the page you are on. That happens directly between your browser and Google.

You can control how Google personalises what you see at My Ad Center, and read how Google uses data from sites that use its services at policies.google.com/technologies/partner-sites. In the UK, EU and Switzerland you are asked for consent before personalised ads are shown.

Typefaces are loaded from Google Fonts, which means Google receives a request from your browser carrying your IP address. The feedback form, when you open it, is hosted by Tally.

This switch stops the milestone messages described above from being sent, and clears the two random identifiers. It is remembered in this browser, so it applies until you clear your browser data or turn it back on.

It does not affect advertising, which is controlled through the links above, and it never affects your saved work.

Questions about any of this, or a request to remove something, can go through the feedback button in the header. Because nothing here is tied to a person, there is generally nothing held that could identify you to remove.