With the new Playground, URLs contain a lot more information about your settings. This makes reproductions accurate, and you don't have to tell someone to hit a particular compiler flag to replicate your setup. The URL contains: - Whether you are on an example - The gzipped source code for your TypeScript/JavaScript - Backwards compatibility for older non-gzipped URLs - Which language you are working in - The diff of your compiler settings from the defaults example:new-compiler-defaults - Your text selection if you have some code highlighted The URL is updated live when any of the above changes using HTML5's replaceState, so your back button will still work as expected. When loading an example, you'll see an occasional e=[number] which is used to ensure the browser correctly reloads when you jump between examples. It's harmless. You can see the URL change on this page by editing some of the comments, or start selecting some text. Pressing reload on your browser will take you back to the same state.