Datestamp completed tasks
When I mark a task as completed, ToDoist should add the date completed. That way, the completed task list becomes a journal of my activities. It would be useful for writing monthly activity reports, for instance. Maybe you could also add the completed task to Google Calendar, then I could see all my appointments and what I did, all in one place! This would be very useful.
This is already available, but it's a Premium feature. With Todoist Premium, aside from the standard access to completed tasks that you have for free, you can click on the Karma score in the top-right corner, go to "View All Completed" and you'll see a full log of all task completion events with dates and times of their completion. You can filter it by date, project, label and even visualize your productivity.
Feel free to try sign-up for Premium, if it won't meet your expectations within 30 days of purchase, you can ask us for a full refund.