# Cronofy alternative for calendar APIs

Source: https://developer.nylas.com/docs/cookbook/calendar/cronofy-alternative/

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.

```bash
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": ["leyah@example.com"]
	}'

```

```python [cronofyFreeBusy-Python SDK]

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](/docs/cookbook/calendar/check-free-busy/).

## 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.

```bash
curl --request GET \
  --url 'https://api.us.nylas.com/v3/grants/<NYLAS_GRANT_ID>/events?calendar_id=primary&limit=50' \
  --header 'Authorization: Bearer <NYLAS_API_KEY>'
```

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](/docs/cookbook/calendar/find-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](/docs/cookbook/calendar/check-availability/) handles the slot math either way.


> **Info:** 
> **New to Nylas?** Start with the [quickstart guide](/docs/v3/getting-started/) to set up your app and connect a test account before continuing here.


## What's next

- [Check Free/Busy status](/docs/cookbook/calendar/check-free-busy/) for raw busy blocks across connected calendars
- [Check calendar availability](/docs/cookbook/calendar/check-availability/) to return computed open slots across attendees
- [Find open meeting times](/docs/cookbook/calendar/find-meeting-times/) for the full availability query with constraints
- [Getting started with Nylas](/docs/v3/getting-started/) to create a project, connector, and your first grant