Offline to-do lists that sync, compared.

Todoist is the clearest. Its help center says you can add, delete and change tasks with no connection, and they sync on their own once you’re back online. Log in before you go offline, and don’t close the app, log out or clear its data until they’ve synced, or the changes are deleted. The article names no plan.

A Microsoft notice about updating the To Do apps says you’ll “still be able to use To Do in offline mode”, and that “any unsynced data will be lost” if you log out.

Google’s Tasks help doesn’t cover offline use; its privacy page says only that tasks you choose to use offline are stored on your device. TickTick promises “real-time sync” and Apple says reminders “stay up to date on all your devices”, but neither says what happens without a signal. That doesn’t mean they stop working, only that it’s worth a test before a trip.

• Todoist Free allows 5 personal projects, 3 filter views, 5 MB a file and 7 days of activity history. Tasks with a date and time get a reminder; custom, location-based and recurring ones are Pro, at $7 a month or $60 a year. Up to 5 people can share a project.
• Microsoft To Do is free with a personal Microsoft account, with no limits stated. Tasks take steps, due dates and reminders, and a list can be shared by an invitation link.
• Google Tasks works with a Google account, in its phone apps, at tasks.google.com and beside Gmail and Calendar. Tasks take subtasks, due dates and notifications, and can be assigned to people in Google Chat.
• TickTick Free allows 9 lists of 99 tasks, 19 checklist items a task, 1 attachment a day and 2 task reminders, and you can share a list with one other person. Premium costs under $4.17 a month, billed yearly.
• Apple Reminders is built into iPhone and iPad and syncs through iCloud with a Mac on the same Apple Account. Reminders take subtasks, due dates and alerts by time or place, and lists can be shared with other iCloud users. A Windows PC gets iCloud.com in a browser; Apple’s pages don’t cover Android.

To-do List is ours, and it isn’t free: it comes with implements, $4.99 a month or $49.99 a year for every tool, with no ads. Every change saves on your device first and syncs after, so it never waits for a signal. Once opened on a device, it works there offline; the first visit needs a connection.

It syncs whenever it’s open and online, including moments after a change and when the connection comes back. An iPhone can’t sync with the app closed, so open it once you’re back online. If two devices changed the same task offline, the most recent change to each part of it wins, so a rename on one and a tick on the other both stay, and new tasks from both are kept, once each.

It’s one list of up to 500 tasks, each with up to 30 subtasks, with no due dates, reminders, projects or sharing, on purpose; if you need those, Microsoft To Do has them for free. If your subscription ends, your list stays open to read, but you can’t change it until you renew.