I think it will be useful to prepare workout without pc client, just in the web.
Been suggested many times
A Zwift community contributor on the Zwift Riders Facebook group has already created a web-based Zwift Workout builder. Search the groups for the link.
Looked, searched - could not find the workout builder you mentioned. Do you have a link?
I didn’t found too, but workout it is simple xml, so you can easily write you own.
https://gist.github.com/anonymous/0fc28e9756616454d8dc here you can find my example