calendar availability api

A calendar availability API is an API that lets software check when someone or something is free or busy, and often to create availability schedules for booking or scheduling.

Common capabilities

• Get free/busy times for a user, room, or resource
• List events in a date range
• Check conflicts before creating a meeting
• Create/update/delete events
• Find open slots based on working hours, time zone, and duration
• Handle recurring events
• Support invitees / attendees
• Manage time zones and daylight saving

Typical endpoints

A scheduling API often includes endpoints like:

• GET /availability?user_id=123&start=...&end=...
• POST /free-busy
• GET /events
• POST /events
• PATCH /events/{id}
• DELETE /events/{id}

Example request

POST /free-busy
{
  "calendar_id": "cal_123",
  "start": "2026-10-15T09:00:00Z",
  "end": "2026-10-15T17:00:00Z",
  "duration_minutes": 30
}

Example response

{
  "available_slots": [
    {
      "start": "2026-10-15T10:00:00Z",
      "end": "2026-10-15T10:30:00Z"
    },
    {
      "start": "2026-10-15T14:00:00Z",
      "end": "2026-10-15T14:30:00Z"
    }
  ]
}

If you want to build one

You’ll usually need:

• authentication/authorization
• calendar data model
• conflict detection logic
• recurring event expansion
• time zone normalization
• rate limiting and sync with external calendars

Existing calendar APIs

Popular ones include:

• Google Calendar API
• Microsoft Graph Calendar API
• Cal.com API (scheduling)
• Cronofy API
• Nylas Calendar API

If you want, I can help you with one of these:

1. Design a custom calendar availability API
2. Use Google Calendar / Microsoft Graph
3. Write sample code
4. Define an OpenAPI spec