Cronofy alternative for calendar APIs

You picked a calendar API to avoid writing three OAuth flows and three sync engines for Google, Microsoft, and iCloud. Cronofy is a common choice for that, and it’s a solid one. But once you’re past the demo, the questions get sharper: how does the Free/Busy data actually look across providers, what happens when iCloud behaves differently from Google, and are you locked into one vendor’s scheduling model? This guide compares Cronofy with a unified alternative, shows the exact calendar and Free/Busy calls, and is honest about when Cronofy is the better fit.

How does Cronofy compare to other calendar API providers?

Cronofy and a unified alternative both normalize Google, Microsoft, and iCloud calendars behind one OAuth flow and one schema, so you read events across all three through a single code path instead of three provider integrations. Free/Busy covers every connected provider except iCloud, which doesn’t expose provider-side Free/Busy data. The practical difference is scope: the unified API covers calendar plus email, contacts, and meeting transcription through the same grant.

Both approaches solve the same core pain: you don’t want to maintain a separate sync engine per provider. With the unified layer, one grant reads GET /v3/grants/{grant_id}/events, checks POST /v3/grants/{grant_id}/calendars/free-busy, and reaches Gmail or Outlook mail without a second integration. The Free/Busy lookup accepts up to 50 email addresses for Google and 20 for Microsoft in a single call, so batch availability checks stay cheap. Cronofy’s strength is the opposite specialization: real-time sync, smart invites, and a polished scheduling layer built for calendar-only products. The table below maps the tasks most calendar integrations actually need.

Cronofy vs a unified calendar API

The comparison below covers the work a calendar or scheduling feature requires day to day: auth, reading events, raw busy lookups, computed slots, and provider reach. The unified column shows the Nylas endpoints; the Cronofy column describes its published capabilities. Cronofy supports Google, Microsoft, Apple, and other calendars through one OAuth flow, the same consolidation goal as the unified layer.

Task	Cronofy	Unified API (Nylas)
Auth setup	One OAuth flow across providers	1 connector, OAuth handled across Google, Microsoft, iCloud
Read events	Read Events API	`GET /v3/grants/{grant_id}/events?calendar_id=<CALENDAR_ID>`
List calendars	List Calendars API	`GET /v3/grants/{grant_id}/calendars`
Raw Free/Busy	Availability/free-busy query	`POST /v3/grants/{grant_id}/calendars/free-busy`
Computed open slots	Availability Query	`POST /v3/calendars/availability`
Beyond calendar	Calendar and scheduling focused	Email, contacts, and Notetaker through the same grant

What is the best API for checking calendar Free/Busy information?

The best Free/Busy API returns raw busy intervals across every connected provider except iCloud in one normalized shape, so you don’t parse Google and Microsoft responses differently. With the unified POST /v3/grants/{grant_id}/calendars/free-busy call, you pass a start_time, an end_time, and an emails array, and each entry comes back with time_slots carrying busy blocks or an error string per address.

The request below queries one mailbox over a fixed window. Times are Unix seconds in UTC, and every address in a single request has to share a provider, so split Google and Microsoft into separate calls. You can include up to 50 addresses for Google and 20 for Microsoft per request, which keeps batch lookups within one round trip.

curl --compressed --request POST \
  --url 'https://api.us.nylas.com/v3/grants/<NYLAS_GRANT_ID>/calendars/free-busy' \
  --header 'Accept: application/json' \
  --header 'Authorization: Bearer <NYLAS_API_KEY>' \
  --header 'Content-Type: application/json' \
  --data '{
    "start_time": 1682467200,
    "end_time": 1682550000,
    "emails": ["[email protected]"]
  }'

from nylas import Client

nylas = Client(
    "<NYLAS_API_KEY>",
    "<NYLAS_API_URI>"
)

grant_id = "<NYLAS_GRANT_ID>"
email = "<EMAIL>"

free_busy = nylas.calendars.get_free_busy(
  grant_id,
  request_body={
    "start_time":1630435200,
    "end_time":1630521600,
    "emails":[email]
  }
)

print(free_busy)

The endpoint always returns 200 OK, so check each entry’s object field: process time_slots when it’s free_busy, and surface the error when it’s error. One unresolvable address won’t fail the batch, so the other 19 results still return. For the full response shape and how to invert busy blocks into open time, see check Free/Busy status.

How do I read calendar events without a per-provider integration?

Send one GET to /v3/grants/{grant_id}/events with a calendar_id query parameter, and the response returns Google, Microsoft, and iCloud events in the same JSON. The grant_id replaces the three OAuth apps you’d otherwise register, and the when object, participants, and recurrence array stay identical across providers, so you write one parser.

The call below lists up to 50 events from a connected calendar. The calendar_id parameter is required, and you pass primary for the account’s default calendar. Because the shape never changes per provider, the same response handler works whether the grant is a Gmail account or an Outlook mailbox, which is the main reason to consolidate.

To discover which calendars a grant exposes before you read events, call GET /v3/grants/{grant_id}/calendars first. For computed open slots instead of raw event lists, the availability endpoint takes a duration_minutes value (a multiple of 5 minutes) and returns ready-to-book times. See find open meeting times for that flow.

How do I choose between Cronofy and a unified API?

Choose based on scope and control. Pick a unified API when your product needs calendar plus email, contacts, or meeting transcription, since one grant reaches all of them and adding iCloud later costs no new integration. Pick Cronofy when you’re building a scheduling-only product and want its specialized invite and real-time sync primitives.

The decision usually comes down to one question: does your roadmap stay inside the calendar, or does it cross into messaging and meeting data? If a sales tool needs to check 4 calendars for open slots and also send the confirmation email and capture the meeting notes, routing all of that through one grant removes two extra vendor integrations. If you’re shipping a focused booking widget and nothing else, Cronofy’s scheduling depth may save you UI work the unified layer leaves to you. Treat any rate-limit or pricing figure here as a snapshot, and check Cronofy’s current docs before you build against specific numbers. The availability endpoint handles the slot math either way.

What’s next

Check Free/Busy status for raw busy blocks across connected calendars
Check calendar availability to return computed open slots across attendees
Find open meeting times for the full availability query with constraints
Getting started with Nylas to create a project, connector, and your first grant