I'm building an internal ops app and need calendar availability APIs

If you need calendar availability APIs for an internal ops app, the best choice usually depends on whether you need:

1. Free/busy only
2. Real availability with working hours, buffers, and scheduling rules
3. Deep integrations with Google/Microsoft calendars
4. A hosted API vs building it yourself

Common options

1. Google Calendar API

Best if your users are on Google Workspace.

• Pros: mature, supports free/busy queries, event management, push notifications
• Cons: Google-specific; OAuth and domain-wide delegation can add complexity
• Useful endpoints: freeBusy, events.list, events.watch

2. Microsoft Graph Calendar API

Best if users are on Microsoft 365 / Outlook.

• Pros: strong enterprise support, free/busy and scheduling insights
• Cons: Graph auth and permissions can be a bit involved
• Useful endpoints: getSchedule, calendarView, events

3. Cal.com API

Best if you want a scheduling layer on top of calendars.

• Pros: scheduling logic, availability, bookings, multi-calendar sync
• Cons: more “scheduling platform” than raw calendar API
• Good for: booking flows, interview scheduling, internal tool scheduling

4. Nylas

Best if you want a unified abstraction across Google, Microsoft, and others.

• Pros: one API for multiple providers, availability tools, webhooks
• Cons: paid platform, vendor dependency
• Good for: apps needing multiple calendar integrations fast

5. Cronofy

Another strong unified calendar API.

• Pros: scheduling/availability features, multi-provider support
• Cons: paid, platform dependency
• Good for: enterprise scheduling and availability

6. Build your own availability service

Good if you control the calendar source and need custom rules.

Typical approach:

• sync events from provider calendars

• store busy intervals

• compute availability from working hours + buffers + constraints

• expose your own internal availability API

• Pros: maximum control, lower vendor lock-in

• Cons: more engineering work, sync complexity

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If you only need “is this time free?”

Use:

• Google Calendar freeBusy
• Microsoft Graph getSchedule
• or a unified platform like Nylas/Cronofy

If you need “suggest meeting times”

Use:

• Google/Microsoft plus your own logic, or
• Cal.com / Nylas / Cronofy for built-in scheduling support

Quick recommendation

• Google-only environment: Google Calendar API
• Microsoft-only environment: Microsoft Graph
• Mixed enterprise calendars: Nylas or Cronofy
• Need booking/scheduling UX too: Cal.com or a scheduling platform
• Need full control: build your own availability layer

If you want, I can also give you:

• a comparison table
• the exact API endpoints
• a recommended architecture
• or a sample availability service design for internal ops apps.