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Calendar availability API
Build apps with real-time calendar availability
Give users the easiest scheduling experience across calendars. The Nylas API syncs schedulers with Google and Outlook, checks group availability, and simplifies coordination across time zones.
Updated November 2026
Calendar availability
What is calendar availability?
Calendar availability is the set of times when people or resources are free to meet. The Nylas Availability endpoint calculates those times across Google, Outlook and other calendars and returns ready-to-offer meeting slots. Designed to help apps avoid double-booking, manage team availability, and simplify global scheduling with minimal custom logic.
- Prevent double booking The Nylas calendar availability API pulls accurate, up-to-date availability from Google Calendar and Outlook Calendar to avoid scheduling conflicts.
- Build on trusted calendar data Create new scheduling apps or improve existing products by adding calendar availability to CRMs, HR tools, or booking platforms with our API.
- Become the go-to for group bookings Build with scheduling logic for finding shared group calendar availability, or round-robins to spread meetings across available users.
How the Availability endpoint works
- Nylas reads each person’s busy times.
- It applies working hours and breaks between meetings.
- It returns the slots that fit, with the people who are free at each time.
You book the chosen slot separately by creating an event.
| Parameter | What it does |
|---|---|
duration_minutes | Length of each slot |
interval_minutes | How often a slot can start. Defaults to duration_minutes |
availability_rules.buffer | before and after minutes to keep free around meetings, 0 to 120 in steps of 5 |
round_to | Rounds slot start times, in minutes. Defaults to 15 |
availability_method | collective, max-fairness or max-availability (default) |
When to use Free/Busy instead
The Free/Busy endpoint returns raw busy blocks per person, for up to 20 people on Microsoft or 50 on Google, all on the same provider. It is not available for iCloud. The Availability endpoint returns meeting-ready slots for up to 50 emails. Use Free/Busy when you want to work out open times yourself.
How does group availability work?
- collective: keep only times when everyone is free. Use it for meetings everyone attends.
- max-fairness: spreads meetings evenly. Nylas offers times for whoever was booked least recently, and falls back to max-availability if they have no free time.
- max-availability (default): offers every time at least one person is free, with whoever was booked least recently first.
See the group availability guide.
Availability features
Build powerful availability features for your app
Compatible with any business app, from startups to enterprises, Nylas makes scheduling a breeze.
Group scheduling support
Check availability across calendars and participant needs without writing custom logic. Nylas handles scheduling automation so you can build a better app experience for your users.
Google Calendar availability
Sync with Google Calendar availability to check user schedules in real-time, ensuring accurate meeting planning.
Outlook Calendar availability
Integrate with Outlook calendar availability to support enterprise users and streamline scheduling.
Time zone support
Handle scheduling across time zones effortlessly. Events scheduled with the Nylas API inherits the time zones you specify, making it a go-to choice for global businesses and distributed teams.
Real-time availability checks
Pull free/busy status for individuals or groups instantly. Support both one-on-one meetings and group bookings across organizations with real-time visibility into both Google and Outlook calendars.
POST https://your-app.com/webhooks/nylas
// Header: X-Nylas-Signature: hmac_sha256=a3f8c2d1e9...
{
"specversion": "1.0",
"type": "event.created",
"source": "/nylas/calendar/events",
"id": "notif_9k3mZx8vL2",
"time": 1718304000,
"retry_config": {
"attempt": 1,
"max_retries": 3,
"backoff": "exponential"
},
"data": {
"object": "event",
"id": "evt_abc123def456",
"calendar_id": "cal_primary_9x2k",
"grant_id": "grant_8f2a4b6c",
"title": "Q3 Architecture Review",
"status": "confirmed",
"provider": "microsoft_office_365",
"when": {
"start_time": 1718304000,
"end_time": 1718307600,
"timezone": "America/New_York"
},
"participants": [
{ "email": "eng@acme.com", "status": "yes" },
{ "email": "pm@acme.com", "status": "maybe" }
],
"nylas_normalized": true
}
}Developers integrate calendar availability in minutes
With the Nylas availability calendar tool , adding availability features to your app is straightforward:
Authenticating users
Create a Nylas account, get your API key, and securely connect to Google, Outlook, and other calendar providers in one seamless integration.
Sync availability across calendars
Use endpoints like Get Availability and Get Free/Busy to see open time slots, handle recurring events, and work across time zones.
Automating scheduling
Use our API to create, update, or cancel meetings. Add meeting information like participants, location and conferencing links.
The Calendar API powering top-tier applications
250,000+ developers trust Nylas to power calendar experiences their customers love.
RecruiterPM saves recruiters 10 hours a week and ships 8x faster
10 hrs
/week saved per recruiter
8x
faster build with 55% fewer resources
“Bringing multiple channels into a single hub powered by Nylas has been a goldmine for user communication.”
TalentReef cut time-to-hire by 3 days and slashed dropoff from 98% to 12%
3 days
faster time-to-hire
98% → 12%
applicant dropoff cut
“There’s no longer any disconnect with users copying and pasting information for scheduling or sending out manual emails. This has made a huge difference in response times.”
Jobylon grew ARR 25% by adding native email and calendar in under a month
25%
YoY ARR growth
10% / 30%
new acquisition / expansion
“Nylas can do the heavy lifting of integrating with proprietary APIs, allowing us to work with a simple, standardized API.”
Jarvis Legal saves law professionals 3 hours a day and lifts upsells 15%
3 hours
/day saved for end users
15%
lift in services sold
“A unified calendaring experience is essential for lawyers to definitively know what event happened for what client at what time. They need to be organized and they often rely on shared calendars.”
Two developers integrated all three Nylas APIs in 22 days — turning LionDesk into the #1 real estate CRM
22 days
to launch
$1.8M
in dev costs saved
“We don’t want to build our own stuff to support all the different versions of Microsoft. Just leave it to the experts.”
Clio saved at least a year of build time on Exchange and Google integration
1+ year
of build time saved
“It would have cost us at least a year to build out just the Exchange and Google integration. By building on top of the Nylas API, the Clio team was able to focus on other core components of their CRM.”
What can you build with Nylas?
You build the features your users want. We’ll handle the calendar infrastructure behind it.
CRM platforms
In CRMs, you can add calendar availability to contact and deal views, enabling sales or support reps to schedule follow-ups instantly.
Client bookings
For client bookings, you can avoid conflicts by syncing with connected calendars and build logic to assign available staff.
Event planners
Event planners can check group availability to coordinate large events and create or update event details programmatically.
Infrastructure Trust & Compliance
Hardened Infrastructure for Sensitive Data
Calendar data is sensitive. We treat it like healthcare data, encrypted at rest and in transit, audited continuously, and governed by strict data residency controls.
99.99%
API success rate
SOC 2
Type II Certified
34.5B
API Transactions
HIPAA
Compliant
Wondering how calendar availability works?
Need more help?
Let’s Talk!
Nylas provides a unified API that normalizes data from Google Calendar, Outlook, Exchange, and other providers. This lets you query and display real-time availability across all calendar systems with one integration.
Yes. You can fetch free/busy data for multiple users at once using our /availability endpoint to display combined availability for teams, departments, or shared resources.
Absolutely. Nylas is SOC 2 Type II, GDPR, and HIPAA compliant. All data is encrypted in transit and at rest, and we follow industry best practices for authentication and authorization.
Yes. The Nylas API lets you define availability constraints like working hours, meeting lengths, buffer times, and more so you can tailor the experience to your users’ needs.
Not necessarily. While you can build a custom UI, Nylas also provides ready-to-use scheduling components that integrate with the availability API for a faster go-to-market.
A calendar availability API returns the times when people are free to meet. The Nylas Availability endpoint does this across Google and Outlook calendars.
Re-check the slot at the moment of booking, not only when you show the slot list, then create the event.
Yes. The Availability endpoint takes up to 50 emails and returns the times when a meeting fits for those people.
Free/busy returns busy blocks. Availability returns open meeting slots with working hours and buffers applied.
Slots are time ranges. Store them in UTC and convert them to each visitor’s time zone in your app.