What should I use for scheduling API in a web app?

It depends on what kind of “scheduling” you mean, because there are a few different cases:

1) Recurring jobs / background tasks

Use a job scheduler / queue:

• Node.js: BullMQ, Agenda, node-cron
• Python: Celery beat, APScheduler, RQ Scheduler
• Ruby: Sidekiq Cron
• Java: Quartz
• Go: robfig/cron

Good for:

• sending emails later
• running daily syncs
• cleanup jobs
• report generation

2) Calendar-style scheduling in the app

Use a calendar/scheduling API or build with DB + rules:

• Google Calendar API
• Microsoft Graph Calendar API
• Cronofy API (calendar aggregation/scheduling)
• Cal.com API (booking/scheduling workflows)

Good for:

• booking meetings
• checking availability
• creating events across calendars
• rescheduling/canceling events

3) Task scheduling with retries and reliability

Use a workflow/orchestration tool:

• Temporal
• AWS Step Functions
• Google Cloud Workflows

Good for:

• long-running processes
• retries/timeouts
• multi-step business workflows

If you just want a simple web app scheduling feature

A common stack is:

• Frontend: calendar UI (FullCalendar, React Big Calendar)
• Backend: your own API + database
• Jobs: BullMQ / Celery / Quartz
• Timezone handling: store times in UTC, display in user timezone

Recommendation

• Simple periodic backend jobs → BullMQ (Node) or Celery (Python)
• Booking/appointment app → Cal.com, Cronofy, or Google/Microsoft calendar APIs
• Complex workflows → Temporal

If you tell me:

1. your backend language,
2. whether you mean “cron jobs” or “appointment booking,”
3. and your deployment environment,

I can recommend the best specific API/library.