The two real integrations: Apple Calendar + Feishu
There are exactly two calendars SnapCal builds a real integration with and can write events into directly: your iPhone's local Apple Calendar (written directly through the system's EventKit framework — no extra account authorization needed, just a one-time "Calendar" access permission in the system prompt), and Feishu Calendar (which requires you to set up a custom app once on the Feishu Open Platform — see the tutorial below). You can check both on a single read and it writes to both at once; if one fails, it doesn't affect the other.
Apple Calendar (on your iPhone)
The first time you use it, the system prompts for calendar access. Once you approve it, SnapCal can create, edit, and delete the events it writes directly. This path needs zero setup — it just works right after you install the app.
Feishu Calendar
Feishu has a slightly higher bar to clear. A Feishu "custom app" is only accessible to the company that created it — SnapCal can't use one official app to handle authorization for every Feishu tenant in the world. So each company (or individual) needs to create their own Feishu app and enter its App ID and Secret into SnapCal. See the related article below for the full five-step tutorial.
About Google Calendar and Outlook: a detail that's easy to misunderstand
Let's be precise here: SnapCal has no separate integration that writes to Google Calendar or Outlook. But if you've already linked a Google account or an Outlook/Exchange account under iPhone Settings → Calendar → Accounts, the system folds the calendars under those accounts into your iPhone's overall calendar list — and when SnapCal writes to "Apple Calendar," those calendars from your linked accounts do show up as selectable options.
This isn't SnapCal doing anything special — it's how Apple's EventKit framework's account system is designed. Any app that writes to the system calendar can see every calendar account you've linked in Settings. In other words, if what you actually want is "the event ends up in the Google Calendar app," you'll get that result as long as you've correctly linked your Google account in iPhone Settings and set it as the target calendar when SnapCal writes the event — but that depends on the account being linked at the system level, not on SnapCal having its own built-in Google OAuth login.
Which one should you use
For personal or family events, just use your iPhone's local Apple Calendar — zero setup, least hassle. For company collaboration or team schedules coming out of Feishu group messages, it's worth spending a few minutes setting up the Feishu integration so both stay in sync without switching apps. For cases where you need both — say, a work meeting that should land in your company's Feishu and also sync to your personal phone calendar — just check both boxes on a single read.
