Everything you need to know about Stellar Calendars.
Getting started
Stellar is a rule-based calendar assistant that works across Google Calendar, Apple Calendar / iCloud, and Outlook / Microsoft 365. You tell it which events to copy and where, and it keeps everything in sync automatically.
Enter your email address and click Send Code. You will receive a 6-digit verification code by email — enter it to sign in. No password is needed.
Once signed in, go to the Account tab to connect your Google, Apple, or Outlook calendars. Connecting a calendar is a separate step from signing in, so you can use any email address as your Stellar account.
Stellar supports Google Calendar, Apple Calendar / iCloud, and Outlook / Microsoft 365. You can create rules between any combination — for example, copy events from a Google calendar to an Apple calendar, or from Outlook to Google.
During the beta period, Stellar is completely free. After the beta ends, a small number of calendars with a limited number of events will stay free. Unlimited access will cost less than the price of a coffee per month.
Connecting calendars
Go to the Account tab and click Connect Google Calendar. You will be redirected to Google to sign in and grant Stellar permission to read and write your calendars.
Go to the Account tab and find the Apple section. Enter your Apple ID (your iCloud email) and an app-specific password — not your regular Apple ID password. Generate one at appleid.apple.com under Sign-In and Security → App-Specific Passwords.
Apple calendars are checked for changes every 5 minutes. Apple does not support instant push notifications, so there is a small delay compared to Google.
Go to the Account tab and click Connect Outlook Calendar. You will be redirected to Microsoft to sign in and grant Stellar permission. Only the permissions needed to sync are requested.
Stellar connects to one Google account at a time. To sync calendars across two Google accounts, share a calendar from the second account to your main account in Google Calendar settings, then Stellar can see it as one of your calendars.
Sync rules
You create a rule that says "copy events from calendar A to calendar B." Stellar watches both calendars and keeps the copies in sync — if the original event is updated or cancelled, the copy is updated or deleted too.
Rules can copy all events, or only events whose description contains a specific hashtag (your choice). See What can Stellar do? for examples.
Yes. You can have one rule copying A → B and another copying B → A. Events will only appear once — Stellar detects its own copies and does not create infinite loops.
Yes. When creating a rule, choose the Busy action instead of Copy. The destination event will show as "Busy" with no title or description — useful for blocking time on a work calendar without revealing personal details.
Yes. In the rule editor you can enter a title template. Available placeholders:
%s — the original event title%c — the name of the source calendar%d — the event start date (YYYY-MM-DD)%t — the event start time (HH:MM)For example, a template of %c: %s would turn "Team meeting" from "Work" calendar into "Work: Team meeting" on the destination.
Your rules are preserved for up to 7 days. If you recreate the calendar with the same name within that window, Stellar automatically relinks your rules to the new calendar and resumes syncing. Events that were already synced to a destination calendar remain there.
Shadow Calendar
The shadow calendar is like a recycle bin for synced events. If you delete a copied event from your destination calendar, Stellar moves it to the shadow calendar instead of permanently removing it — so you can restore it later if you change your mind.
To restore an event, delete it from the shadow calendar. Stellar will move it back to where it came from.
Example: Suppose you sync your running club's race calendar onto your personal calendar so you can see upcoming events. You decide to skip one particular race and delete its copy. Instead of disappearing entirely, it moves to the shadow calendar. If you later decide to run it after all, delete it from the shadow calendar and it reappears on your personal calendar.
Each calendar type gets its own shadow calendar. Most calendar apps let you hide a calendar from the sidebar if you don't want to see it cluttering your view.
Advanced features
Add #stellar-series to any event's description, then list your dates using #event: lines. Stellar generates a separate calendar event for each entry. See the features page for full examples and the hashtag reference for syntax details.
Add #stellar-train plus a distance tag (#marathon, #half, #10k, or #5k) and #goal:H:MM to a race event on your Google Calendar. Stellar generates a full training schedule from today through race day, adapting automatically if you change your goal or race date. See the hashtag reference for all available options.
Stellar only looks for #stellar- hashtags on calendars it's set to scan. A calendar is scanned automatically when it's the source of a sync rule, or when it already has a Stellar series or plan on it. For any other calendar, turn on the “scan” checkbox next to it under Your Calendars on the dashboard, and Stellar will pick up the tags on its next sync.
Un-check the “scan” checkbox next to the calendar under Your Calendars. Stellar removes the series and training-plan events it generated on that calendar — the same way disabling a sync rule cleans up its copies. Your own master/race events stay put, so re-checking “scan” later regenerates everything.
Privacy & data
No. Stellar never stores the content of your calendar events. It reads your calendars and only keeps calendar names and event IDs — the minimum needed to copy events and detect changes. Your event titles, descriptions, and times stay on your calendars and are never stored on Stellar's servers.
Every event created by Stellar includes a line in its description beginning with https://StellarCalendar.com/
From the Account tab, select Delete account. All your rules and connected calendars are removed. You can recreate your account later if you wish.