Yes, all mandatory fields which must be completed with values in order to proceed with the save are marked with an asterisk or alternatively a red banner will appear or the text will be highlighted in red. Additionally, WIPO Sequence does not allow saving of a feature particular if a mandatory qualifier does not have a value, and cannot be empty.
In terms of optional fields, there are various checks conducted during validation and there may be a warning generated which prompts the user to take action or check to see if a particular field is necessary.