Change one of the current user’s reminders: reword it, move when it fires, or mark it done. Get the reminderId from ListReminders or CreateReminder. Pass only the fields you are changing; anything omitted is left alone. At least one must be given. - Snooze or reschedule: set remindAt - Mark done: completed: true — the user has dealt with it and it leaves their active list - Reopen: completed: false - Reword: set description Marking done is the normal way to clear a reminder the user has handled, and it is reversible: the reminder drops out of the default ListReminders results but is still there, readable with completed: true and restorable with completed: false. Reach for DeleteReminder only when the user wants the reminder not to exist; that cannot be undone. Two things this tool will not do. It cannot change what a reminder is attached to — create a new reminder and delete this one instead. And setting remindAt on a repeating reminder replaces the repetition with that single firing, so only do it if the user asked to stop it repeating. ## Times are UTC — convert both ways Timestamps are absolute instants, in and out, while the user asks in their own timezone. Getting this wrong silently sets the reminder to the wrong hour. - In: resolve their wording against their local time, then convert. For America/New_York (UTC-4 in August), “3pm tomorrow” on 2026-08-12 is "2026-08-13T19:00:00Z", not "2026-08-13T15:00:00Z". - Out: report the response’s UTC value back in their timezone — "2026-08-13T19:00:00Z" is “3:00 PM tomorrow”. Ask for their timezone rather than assuming UTC.