You keep a work calendar and a personal one, and neither knows about the other. Both tools copy busy time between them — they just charge and connect differently.
SyncThemCalendars covers Google, Outlook and iCloud and meters by sync count. Keeper.sh reaches CalDAV and .ics too, charges $5 flat however many connections you run (or free to start), and copies busy time while event titles stay behind by default.
Does Keeper.sh keep both calendars showing the same busy time?
Yes. Each Keeper.sh connection copies busy blocks one way, so you add one mapping each way (A to B and B to A) when both calendars should stay in step. Guest lists are never copied. Signed-in iCloud on one Apple ID can be source and destination the same way; a pasted share link or subscribed feed is pull-only and cannot be a destination.
SyncThemCalendars offers a one-toggle mirror on each sync (their sync direction page). Same busy-block result on your calendars; one more step at setup on Keeper.sh. The free plan's three connections cover one mirrored pair plus one more calendar going one way.
Which calendars does each one connect?
SyncThemCalendars supports Google Calendar, Microsoft Outlook and Office 365, and Apple iCloud. Their FAQ lists those three, and we could not find any mention of generic CalDAV on their site.
Keeper.sh supports Google, Outlook, iCloud, Fastmail and any CalDAV server. That last part is the difference. If your calendar lives at mailbox.org, Posteo, Nextcloud, Infomaniak or a server you run, Keeper.sh can read and write it.
Keeper.sh also reads iCal and ICS links. Those links are read-only by design, so nothing can write back to them.
If your calendars are all Google, Outlook or iCloud, none of this affects you.
How fast does a change reach your other calendar?
Their sync direction page says "Google and Outlook notify us the moment something changes, so copies update in moments." For iCloud, the same page says they check "every few minutes" (Apple iCloud sync).
On Pro, Google and Microsoft notify Keeper.sh the moment an event changes, so the copy is written within seconds. iCloud, Fastmail and other CalDAV calendars are read on a timer instead, because Apple publishes no way for a calendar tool to be told an event changed. On Free, linked calendars update about every 30 minutes.
On iCloud, neither product is instant. Apple publishes no way for a calendar tool to be told an event changed, so every product in this category checks iCloud on a timer.
What does each one cost?
SyncThemCalendars charges by how many syncs you run, and does not charge for connecting more calendars or accounts (pricing / compare). Their three tiers each cover one user, with a 14-day free trial.
| Keeper.sh | SyncThemCalendars | |
|---|---|---|
| Free plan | 2 linked accounts, 3 connections, no card | 14-day trial, no card |
| Entry paid plan | $5/month, unlimited connections | $3.99/month, 5 syncs |
| Middle plan | None | $7.99/month, 16 syncs |
| Top plan | None | $17.99/month, 36 syncs |
| Yearly option | $45/year | $47.88, $95.88, $215.88 |
Paying monthly, run five syncs or fewer and they are cheaper by a dollar. Run more than five and we are cheaper, because $5 on Keeper.sh Pro has no connection limit at all.
Paying yearly there is no crossover. Keeper.sh Pro is $45 a year against their cheapest $47.88, because their yearly price is just twelve monthly ones.
The other real difference is the free plan. Ours never expires, with 2 accounts and 3 connections. Theirs is 14 days, and then they ask for payment.
Where Keeper.sh fits better
More calendar types. CalDAV and Fastmail, as above.
It is open source. Keeper.sh is AGPL-3.0. The sync engine is on GitHub and you can read it before trusting it with your calendar.
You can run it yourself. Every paid feature is free on your own instance. See below.
Unlimited connections for $5. No counting syncs.
Your event details stay put by default. A new connection copies a busy block titled after the calendar it came from, leaving the title, description and location behind. Pro is what shows the real detail.
An API and an agent connector. Keeper.sh has a REST API, plus an MCP server with 14 tools, so assistants like Claude can list, create, edit, delete and RSVP to events. Both run on the free plan, capped at 25 requests a day, and uncapped on Pro. Docs at /docs/mcp.
One feed for every calendar. Keeper.sh gives you a single private iCal link combining the calendars you choose to include, readable by anything that takes a calendar feed.
What SyncThemCalendars has that Keeper.sh does not
One-toggle mirror. They can mirror a pair with one switch on a sync (two-way calendar sync). Keeper.sh uses two mappings for the same busy-block result. Their Google and Outlook copies update "in moments" by their own pages.
Seven languages — English, French, German, Japanese, Spanish, Italian and Portuguese. Keeper.sh is English only.
A lower monthly price at five syncs or fewer, $3.99 against Keeper.sh Pro at $5.
Privacy set per sync and per field, where Keeper.sh sets it once on the calendar events come from.
What about data handling?
SyncThemCalendars does not publish a DPA or a security page that we could find. Their privacy policy, dated March 2019, says data is "stored and processed in United States, or where we or our partners, affiliates and third-party providers maintain facilities."
Keeper.sh publishes no data processing agreement for the hosted service. If your employer requires a signed one, run Keeper.sh on your own server instead. Your database, your server, and nobody else in the path to sign an agreement with.
Running Keeper.sh yourself
Running Keeper.sh yourself gets you the full product. Every Pro feature switches on automatically, including per-minute writes and the uncapped API.
Take this route when the data cannot leave your control. You hold the database, the tokens and the logs, and nobody else sits in the path.
It is genuine work. You need Docker and Docker Compose, Postgres, Redis and a domain, plus your own Google and Microsoft applications, which is the fiddliest step.
Most people should use hosted Keeper.sh at $5 a month. Self-hosting is there when you need it, and the repository has the full guide.
FAQ
Which should I choose?
Keeper.sh, when your calendars go beyond Google, Outlook and iCloud, you want a free start with flat $5 busy-block sync, event titles kept off the copy by default, or a copy you run yourself.
Their one-toggle mirror, two-minute setup, seven languages, and $3.99 entry price are real — they just do not change the CalDAV reach or flat-price story above.
Does Keeper.sh only update every 30 minutes?
No. On Pro, Google and Outlook copies land within seconds. On Free, linked calendars update about every 30 minutes. iCloud and CalDAV stay on a timer on every plan.
Other comparisons
Still weighing tools? These cover the rest of the field.
- Keeper.sh vs CalendarBridge
- Keeper.sh vs Kalender Sync
- Keeper.sh vs Morgen
- Keeper.sh vs OneCal
- Keeper.sh vs Reclaim.ai
- Keeper.sh vs SyncDate
- Nine calendar sync tools compared on price, speed and privacy
Sources
Everything above about SyncThemCalendars comes from their own public pages, checked on 14 September 2026:
- syncthemcalendars.com — homepage, pricing and FAQ
- Two-way calendar sync — sync direction, update speed and privacy fields
- Apple iCloud calendar sync — iCloud checking interval
- Google calendar sync — instant updates from Google
- Compare — pricing model
- Privacy policy — data storage location
Prices and features change. If something here is out of date, their page wins, and we would appreciate you telling us.