# FAQ (https://www.cal-sdk.com/docs/faq)

## What is calsdk? [#what-is-calsdk]

calsdk is an open source TypeScript library that gives your app one API for many calendar providers. You create a provider, such as `google({ accessToken })`, and pass it to plain functions like `listEvents`, `createEvent`, `findFreeTime` and `syncEvents`. Every provider returns the same event shape, so switching calendars changes one line. See the [overview](/docs).

## Which calendars does calsdk support? [#which-calendars-does-calsdk-support]

Google Calendar, Microsoft Outlook and Microsoft 365, iCloud, Zoho Calendar and any other CalDAV server (such as Fastmail, Nextcloud and Radicale), Zoom, Cal.com, Calendly, and ICS feeds, which are read only. There is also an in-memory mock calendar for tests. The providers don't all support the same things: [compare providers](/docs/providers) shows what each one can do.

## Is calsdk a hosted service like Nylas or Cronofy? [#is-calsdk-a-hosted-service-like-nylas-or-cronofy]

No. Hosted calendar APIs run the integration on their own servers: your app calls their API, and they hold the connection to each calendar. calsdk is a library that runs inside your app and calls Google, Microsoft and the others directly, with tokens your app passes in. It has no server, database or queue of its own, so your users' calendar data doesn't pass through anyone else.

## Does calsdk handle OAuth? [#does-calsdk-handle-oauth]

No. calsdk doesn't run OAuth flows or refresh tokens, because your app owns the user's account and so it owns the tokens. Pass a token, or a function that returns a fresh one: calsdk calls it before each request, so you can refresh and cache tokens however your app already does. See [Install](/docs/installation#keep-credentials-on-the-server).

## Where does calsdk run? [#where-does-calsdk-run]

Anywhere with `fetch`. Every package is ESM only and talks to provider APIs with `fetch` and nothing else, so it runs on Node.js 20 or later, Bun, Deno and edge runtimes. Create providers in server code, since their tokens give full access to a user's calendar.

## How do I find a free time across Google Calendar and Outlook? [#how-do-i-find-a-free-time-across-google-calendar-and-outlook]

Call `findFreeTime` with calendars from any mix of providers, and it returns the slots when all of them are free. If one calendar can't be read, it throws `FreeBusyUnavailableError` instead of offering times that might clash. See [Find free time](/docs/guides/free-time).

## How does calsdk handle recurring events? [#how-does-calsdk-handle-recurring-events]

You create a series with an RRULE, and listing expands it into occurrences, each with its own id. To change one, pass its id to `updateEvent` or `deleteEvent` with a scope: `'this'` for that occurrence only, `'thisAndFollowing'` for it and every later one, or `'all'` for the whole series. Not every provider has every scope (Outlook has no "this and following"), and the provider pages say which. See [Recurring events](/docs/guides/recurring-events).

## What happens when a provider can't do what I asked? [#what-happens-when-a-provider-cant-do-what-i-asked]

If the call can still do what you meant, calsdk saves what it can and returns `warnings` that say what it couldn't, such as an event color the provider doesn't have. If going ahead would save a different schedule or lose data, it throws `UnsupportedFunctionalityError` instead. It never quietly changes your data. See [Warnings](/docs/concepts/warnings).

## How do I keep a copy of a calendar in sync? [#how-do-i-keep-a-copy-of-a-calendar-in-sync]

Call `syncEvents`, apply the changes it returns, and save its `nextCursor`. The next call with that cursor returns only what changed since. If the provider expires the cursor, `syncEvents` throws `SyncCursorExpiredError`, and you start over without one. See [Sync changes](/docs/guides/sync).

## Can I test my code without a real calendar account? [#can-i-test-my-code-without-a-real-calendar-account]

Yes. `@cal-sdk/mock` is an in-memory calendar that works with the same functions, with no account and no network, so your tests run offline and fast. See [Test your code](/docs/guides/testing).

## Is calsdk free? [#is-calsdk-free]

Yes. calsdk is open source under the MIT license, and the code is on [GitHub](https://github.com/vkpdeveloper/calsdk).