The editor saves a single page of code stored in the database which the service operates with. Upon update, the service is updated unless there is design time errors, runtime errors will report back just the same. Any line that is an error will highlight with red.
Additionally minimal debugging can be achieved using the single like evaluation and execution entry. Simply click on the entry bar, and use type a "!" for a statement or type a "?" for evaluation, then enter your code and hit enter. Evaluation will return value.