BabyGeezer:
(or is it a case of being wary of installing things - having been scared sh*tless by Mircosoft....)
Except if you actually want to upload the code to your Arduino board you still need to install the plugin for the Arduino Web Editor to your computer, which I've actually had more trouble with than the regular IDE (though to be fair that was in the earlier days of the Arduino Web Editor and I haven't had another try at the plugin since). You can write code, compile code, and share code via the web editor without installing anything.