What does the u/0 in a Gmail URL mean?

It is the position of the account in your signed-in list. mail.google.com/mail/u/0 is the first account you signed in with (your default), u/1 is the second, and so on. You can bookmark these URLs to jump straight to a specific inbox, but the numbers reshuffle if you sign out and back in, in a different order.

Why do Google links keep opening in the wrong account?

Links that do not specify an account open in your default account, u/0, which is whichever account you signed into first in that browser session. If a shared doc or calendar invite belongs to a different account, you get a permission error. Fixes: sign in to your most-used account first so it becomes u/0, edit the link's u/ number, or keep each account in its own browser profile or isolated session so there is no shared default at all.

Can I stop my Gmail accounts from signing each other out?

Not with the built-in account switcher, because all accounts share one browser session; signing out of one signs out all of them, and a security re-check on one can interrupt the rest. To make accounts truly independent you need separate cookie stores: Chrome profiles, different browsers, or an app that gives each account an isolated session, such as Orbit for Mac.

What is the fastest way to switch between many Gmail accounts on a Mac?

For two accounts, the built-in switcher or bookmarked u/0 and u/1 URLs are fine. For three or more, most people end up with either Chrome profiles (free, but one window per account) or a dedicated app. Orbit for Mac keeps every account loaded in one window, each in its own isolated session, and switches with Cmd-1 through 9.

How to Switch Between Gmail Accounts, Every Way Ranked

There are six real ways to switch between Gmail accounts, and they are not interchangeable. They differ in the one thing that matters: whether your accounts share a session or each get their own. Shared-session methods are quick to set up and fall over in identical, predictable ways. Separate-session methods are sturdier and cost you something else instead, usually window clutter or money.

Here is every method, what it actually does with your cookies, and the point at which it breaks. The honest summary up front: methods 1 and 2 are fine for two accounts, methods 3 and 4 carry you to three or four, and past that you are in dedicated-app territory, which is method 6 and, yes, where the app we make lives. It is at the end, and everything before it stands on its own.

1. The built-in Gmail account switcher

Click your avatar in Gmail's top-right corner, choose Add another account, sign in. Every signed-in account now appears in that avatar menu, and you flip between them with two clicks.

What Google is doing underneath: all of those accounts live in one shared browser session, one cookie jar with a stack of identities in it. That single fact produces every symptom people complain about:

Sign out of one, sign out of all. There is no per-account sign-out. One shared session means one shared exit.
The default-account problem. The first account you signed in with becomes the default, and every Google link that does not specify an account opens there. This is why a colleague's doc keeps landing in your personal account and showing a permission error.
One security re-check interrupts everyone. When one account triggers a re-verification, it happens inside the session all of your accounts share.

Verdict: perfect for two accounts you check casually. Increasingly haunted from three up.

2. The u/0 URL trick (the switcher, minus the clicking)

Look at Gmail's address bar: mail.google.com/mail/u/0/. That u/0 is the account's position in your signed-in list. Your second account is u/1, the third u/2, and so on. Which means you can skip the avatar menu entirely:

Bookmark each inbox. mail.google.com/mail/u/0 for work, u/1 for personal. One click, straight into the right inbox. It works for Calendar and Drive too: calendar.google.com/calendar/u/1.
Fix a wrong-account link. When a doc opens in the wrong account, edit the u/ number in the URL and reload. Faster than the account-picker dance.

Two caveats. The numbers are positional, so if you ever sign out and back in, in a different order, every bookmark quietly points at the wrong account. And this is still the same shared session as method 1, with all the same failure modes. It is a better steering wheel on the same car.

Verdict: the best free upgrade if you stay with the built-in switcher. Learn it even if you use nothing else here.

3. Chrome profiles (real isolation, free)

Chrome's profile menu (your avatar, top-right of the browser) creates genuinely separate browser identities: separate cookies, separate extensions, separate histories. One Gmail account per profile means the accounts cannot touch each other. No shared default, no collective sign-out, no cross-account surprises. This is the correct free answer, and Google's own.

The price is geography. Every profile is its own Chrome window, identical in the Dock, all titled “Inbox.” At two or three profiles this is fine. Past that, you spend real minutes a day just locating the right window, and ⌘-Tab stops meaning anything. We wrote up how that plays out at the extreme in running 9 Gmail accounts in Chrome.

Verdict: right answer for 2 to 4 accounts if the window sprawl does not bother you.

4. A different browser per account

Safari for personal, Chrome for work, Firefox for the side project. Total isolation, zero setup beyond signing in, and each browser looks different enough that you always know where you are.

It simply does not scale. There are only so many browsers you are willing to keep updated, each one is a full separate app eating memory, and notification settings multiply. It also quietly assigns each account a whole personality, which is charming until you need a fourth.

Verdict: a fine accident that many people back into. Ceiling of about three.

5. Private windows (the guest pass)

A private or incognito window is a blank session: sign into any account, and when the window closes, the session evaporates. For checking a rarely-used account without disturbing your main setup, or using someone else's machine, it is exactly right.

As a daily method it is self-punishing: you re-sign-in, with two-factor, every single time. Nothing persists. That is the whole point of the feature, and the whole reason it is not a solution.

Verdict: a tool for exceptions, not a system.

6. A dedicated multi-account app

When the account count is real, five, seven, nine, all the free methods converge on the same tax: either a shared session that tangles accounts together, or true isolation smeared across a desktop of identical windows. Dedicated apps exist to give you both halves at once: isolation and one window. There are three genuinely different kinds, and we compare them honestly elsewhere: workspace browsers like Shift and Wavebox (breadth: every web app in one shell, subscription, Chromium underneath), native API clients like Mimestream (Gmail rebuilt as a beautiful Mac mail app, $49.99 a year, mail only), and the approach we took with Orbit, which this site is about, so discount accordingly.

Orbit runs the real Gmail, Calendar, Drive, and Meet, nothing rebuilt, and gives every account its own permanently isolated session in one quiet native window. Switching is ⌘1–9, the way it always should have been: work is ⌘1, personal is ⌘2, the client is ⌘3, muscle memory instead of window-hunting. Search fans out across every account at once. The download is about 12 MB, it is a one-time purchase ($89), and the 14-day trial does not ask for a card. It requires macOS 14 or later on Apple silicon.

Verdict: when you are past four accounts and the free methods have started costing you time or a misdirected email, this category, whichever app you pick from it, is the fix.

The honest decision table

2 accounts, casual — built-in switcher plus the u/ bookmarks. Free, fine, done.
2–4 accounts, daily — Chrome profiles. Real isolation, costs you window sprawl.
Rarely-used extras — private windows, as needed.
5+ accounts, or one wrong-sender scare too many — a dedicated app. Merged-inbox people: Mimestream. Every-web-app people: Wavebox. Real-Gmail-times-N people: Orbit.

Whatever you pick, do the u/0 trick today. It costs nothing, and it is the difference between fighting Google's default-account logic and quietly steering it.