Googleカレンダーの同期 alternatives: what you can drop

Connecting a Google account to a Mac calendar takes under a minute, and the usual result is that every calendar on that account arrives at once, each one with full read and write access. Nothing about that is wrong. It is simply a much larger grant than most of those calendars need, and the excess never announces itself until an event gets dragged by accident on a calendar somebody else owns.

The word sync covers three different mechanisms that behave nothing alike. Sorting out which one each calendar actually requires is the whole of this decision. What follows is the list of things that can be swapped for something lighter, the list of things that cannot, and the order to move them in.

Three mechanisms, one word

The first is two way sync. An account is connected, and events created on either side appear on the other. Creating, moving, deleting, and replying to invitations all travel in both directions.

The second is a read only subscription. Each Google calendar publishes a private address, and pasting that address into another app pulls the contents one way. What is visible looks nearly identical to the two way case. What differs is that local edits do not stick. Delete an event in the subscribing app and it reappears on the next fetch, because the fetch is the only source of truth.

The third is export and import. Events are written to a file and loaded into another calendar, at which point the copy has no relationship to the original. Changing either side changes nothing on the other. This is duplication, not sync, and it belongs to migrations rather than to daily use. Run it as a standing arrangement and cleaning up duplicates becomes a permanent chore.

Telling them apart takes one test: try to create an event on the calendar in question from the Mac app. If it saves and survives the next refresh, that calendar is on a two way connection.

Only two routes exist

Before deciding what to replace, it helps to know how short the menu is.

Google カレンダーを別のカレンダー アプリケーションで表示する方法は 2 つあります。カレンダーを追加して他のアプリケーションで表示できるほか、一部のアプリケーションでは予定を編集することもできます。 出典: support.google.com

Connect with the account, or subscribe with the private address. That is the entire set. The private address lives in the calendar's own settings, under the section for integrating the calendar, and it is a secret in the practical sense: anyone holding the string can read the calendar without signing in to anything. Resetting it invalidates every copy that was ever handed out, including the ones on other devices, and issues a new one.

Calendars that never needed write access

The replacement work starts by going through the sidebar one row at a time and answering a single question: does anything ever get created here by hand.

Four categories almost always answer no. Holiday calendars. Calendars shared by other people for reference. Team rosters, on call schedules, and room availability. Feeds published by outside services, such as fixture lists or filing deadlines. None of these are authored locally, so the ability to edit them is dead weight that occasionally causes damage.

What remains is usually one or two calendars: a work calendar and a personal one. Those are the rows that justify an account connection. Every other row can move to a subscription, and the moment they do, the set of calendars a local app is able to modify shrinks to the set the person actually writes on.

What the Apple Calendar route never had

Some functions are not candidates for replacement because that route never carried them. Google documents three Google Calendar features as unavailable once an account is added to Apple Calendar: email notifications for events, creating a new Google calendar, and room booking.

These are not faults to be diagnosed. They are absences to be routed around, and the routing goes the other way from what the word replacement suggests. Leave email notifications configured on the Google side and treat the Mac app as a place to read and enter events. When a new calendar is needed, create it on the web and then add it to the set that syncs down. Book rooms on the web for the meetings that need them.

Counted honestly, none of these are daily actions. New calendars get created a few times a year. Room booking matters on office days. Opening a browser tab for something that happens once a month is a smaller cost than giving up the parts used every hour.

The substitution table

Current arrangement	Mechanism in use	Lighter replacement	What it costs
Reading a team roster	Two way sync	Private address subscription	Local editing
Showing holidays or fixtures	Two way sync	Public subscription address	Nothing
Telling someone when you are free	Calendar sharing	An appointment booking page	Their view of the whole week
Handing over a schedule as a document	Calendar sharing	An exported file	Any future updates
Reserving a room	The local app	The web interface	One extra place to go

The rightmost column is the price. Working down from the rows where that column is empty or close to it is what keeps this from going wrong.

The booking page in the third row deserves more attention than it gets. It shares no calendar at all: the other party opens a URL, sees open slots, and picks one. Scheduling completes without a sharing grant ever existing, which also means there is nothing left behind to revoke six months later.

Two kinds of address, and why the distinction matters

Both replacement routes in the table above hand out a URL, and they are not the same URL. Mixing them up is the one mistake in this whole exercise that has consequences outside your own machine.

The private address is the one described earlier: a secret string that grants read access to whoever holds it, with no sign in and no record of who is holding it. It is meant for pulling a calendar into an app that only needs to display it, and Google's own guidance on it is to share it with nobody.

The public address is different. It exists only once a calendar has been deliberately made public, and at that point the calendar can be found through search and used by other applications. For a schedule of published events, office hours, or a release timetable, that is the correct tool and the private address is the wrong one. For anything internal, the reverse.

The failure mode is specific and worth naming. A private address handed to a colleague as a convenience does not appear on any sharing list, cannot be revoked for that person alone, and survives them leaving. A sharing grant made through the normal dialog appears in a list, is revocable per person, and is visible to anyone auditing the calendar later. When the goal is to let a particular named person read a calendar, the sharing dialog is the correct instrument even though pasting an address feels faster.

Confirming the swap actually held

A substitution that silently did not take effect is worse than not attempting it, because the assumption of safety is now wrong. Two checks settle it.

First, try to create an event on a calendar that was moved to a subscription. It should refuse, or accept and then lose the event on the next refresh. If it saves and stays, that calendar is still on the account connection and the old grant is intact.

Second, look at the calendar list on the Google side and compare it against the sidebar. A calendar that was meant to stop coming down through the account but is still listed there is being delivered twice, once through the connection and once through the subscription, which is the usual origin of duplicated entries after a reorganisation. Removing one of the two routes resolves it.

Both checks take a minute and they are worth repeating after any later change to the account, since adding a new calendar on the Google side can quietly reinstate the wider arrangement.

Where substitution stops

Some behaviour only exists on a two way connection, and moving those calendars to a subscription fails silently, which is the worst way for something to fail.

Replying to an invitation is the clearest case. Accepting or declining writes to the organiser's calendar, and a read only route has no way to send it. Marking attendance on a subscribed meeting produces nothing on the organiser's screen. The reply looks sent and is not.

Reminders change character too. A reminder added locally to a subscribed event is stored only on that machine and disappears with it. Nothing about it reaches Google or any other device.

Timing is different as well. An account connection is limited by the fetch interval configured locally. A subscription adds the publisher's own update cycle on top of that. If something decided this morning has to be visible to somebody else today, a subscription is the wrong mechanism.

Change notices vanish quietly. On a two way connection, an organiser moving a meeting pushes that change through. On a subscription, the new time simply appears, with no signal that it used to be something else. For a calendar belonging to somebody whose schedule shifts often, that difference matters more than it sounds.

Moving in order

Changing everything at once makes the result unreadable. One row at a time, starting with the rows that cost nothing.

Holidays and external feeds go first, since the chance of ever writing to them was zero. Reference calendars shared by colleagues go second. At that point the local app can write only to the calendars their owner actually writes to.

Then run it for one week and count the number of times something could not be edited that needed editing. Zero means the arrangement is finished. One or two means those specific calendars go back to a two way connection, and only those. The value of moving row by row is that the answer comes back at the level of individual calendars rather than as a single yes or no.

More often than not, every instance of that problem turns out to sit on the same calendar, which settles the question: exactly one connection needed to be two way.

A week is long enough for the answer because the pattern repeats weekly. Recurring meetings, the day the roster gets updated, the evening something personal goes in: all of them come round inside seven days. Running the trial for a month produces the same answer and delays the decision by three weeks.

What to change first

Open the sidebar, mark every calendar that has never received an event typed by hand, and move those to subscriptions before touching anything else. Once the write path is narrow, the remaining friction is not about sync at all but about how fast an event gets recorded in the first place, which is the problem Caltimate is shaped around. The mechanics of entry are set out in entering events, and the gaps between meetings that no sync setting can fix are covered in travel time.