Free Flow Script Editor in Zoho CRM

Free Flow Script Editor in Zoho CRM

Is it possible to directly edit scripts for Custom Functions in Zoho CRM, or is it required to use the Script Builder. I find the Builder very difficult to use and limiting, and it is full of bugs. I get one or two pop up errors every time I open it, and it only let's me use it about 1/3rd of the time. Otherwise I have to close and reopen the window.