Start with who is booking whom. If clients, customers or candidates book time with you, you need a booking page. If you are trying to fit your own work around meetings, you need a calendar assistant. If five busy people need one shared slot, you need a group poll. If you run shifts for hourly staff, you need a rota app, and if people book rooms or desks, you need a space booking tool. Many people need two of these, and few tools do all of them well.
Next, check the calendars. Every tool here works by reading your free and busy times and writing new events back. Make sure it connects to the calendar your organization actually uses, Google or Microsoft, and look at whether it can check several calendars at once. A consultant with a work and a personal calendar, or a team with shared calendars, will hit double bookings if the tool only sees one.
Then look at the rules you need. Booking tools differ most in the details: buffer time between meetings, a limit on bookings per day, minimum notice, intake questions, deposits or payments, and round-robin rules for teams. Write down the three rules you can't live without and test them on the free plan or trial before you pay.
For AI calendar assistants, give the tool a real week. They plan your tasks and focus time around meetings and move blocks when your day changes, but they only work if you feed them honest task lengths and priorities. If you spend more time correcting the plan than following it, try a simpler planner.
For staff scheduling, think about the people who will use it on their phones. Shift workers need to see their schedule, swap shifts and request time off without calling a manager. Check the time clock, the payroll export for your country and whether labor costs show while you build the week.
If you work with people in other countries, check time zone handling on the visitor's side. A good tool shows each person the times in their own zone, handles daylight saving changes and puts the correct zone in the calendar invite.
Finally, read the permissions screen. A scheduling tool can usually see the titles, attendees and locations of everything on your calendar. Check where data is stored, who at your company can see bookings and how to disconnect the tool if you stop using it.