Tasks
Keep a to-do list next to your calendar. Tasks live in task lists: everyone has Tasks, and you can make more (from a task app, or over JMAP).
In webmail
Open the calendar (the calendar button at the top). Under Tasks on the left are your open tasks, soonest due first:
- Add a task: type it under the list, choose a due date if it has one, and choose Add task. A due date means 5 pm that day, in your time zone.
- Tick it off: select the box next to it. It is marked completed and leaves the list.
Overdue tasks say Was due in red.
In task apps
Apps that keep tasks over CalDAV see your task lists as lists of reminders or to-dos, next to your calendars: Apple Reminders, Thunderbird, and DAVx⁵ with a tasks app such as jtx Board or Tasks.org on Android. Set them up as in Calendar and contacts apps; the same account brings both calendars and task lists.
- A list made in the app (Reminders' Add List) becomes a task list.
- Due dates, notes, priority, how far along a task is (percent) and whether it is done travel both ways.
- A task list holds only tasks, and a calendar only events.
- Your Tasks list cannot be deleted; others can, with their tasks.
Sharing
Task lists are your own. Someone you share your whole mailbox with sees them too (and can change them if they may change your mailbox; see Sharing). Lists are not shared one by one, and teams have no task lists.
For developers
JMAP for Tasks (urn:ietf:params:jmap:tasks): TaskList/get, /changes, /set (with onDestroyRemoveTasks), and Task/get, /changes, /set, /query, /queryChanges. Tasks are JSCalendar Task objects (RFC 8984 section 5.2): title, start, due, timeZone, estimatedDuration, progress (needs-action, in-process, completed, failed, cancelled), percentComplete, priority, keywords, recurrenceRules, plus taskListId and the computed utcStart and utcDue. Changing progress sets progressUpdated. Task/query filters by inTaskLists, progress, hasDue, before and after (due, UTC), title, description, text and uid, and sorts by due, start, title, priority, created or updated. The default list has role: "inbox".
Over CalDAV, task lists are calendar collections whose supported-calendar-component-set is VTODO; MKCALENDAR with only VTODO in that set makes one.