Do I need the Yahoo app or Account Key for 2-step verification?

No. Yahoo offers prompts in its own apps, but also accepts codes from any authenticator app. The Authenticator extension reads the QR code straight off the Account Security page and generates the codes in Chrome. Account Key has to be off before 2-step verification can be turned on.

My mail app stopped signing in after I turned on 2-step verification.

Desktop mail programs such as Outlook or Apple Mail cannot ask for a code. On the Account Security page, generate an app password and enter it in the mail program instead of your normal Yahoo password.

What if I lose access to my authenticator?

Use the recovery code if Yahoo gave you one, or the recovery methods on the account, to get back in — then set the authenticator up again. That is why Yahoo asks for two recovery methods before you start, and why keeping the extension’s automatic backups on matters.

Why does Yahoo say my code is wrong?

Usually the computer clock is off by a minute or more. Turn on automatic date and time and try the next code. If it still fails, remove the account from the extension, turn 2-step verification off and on again, and add the new QR code.

Yahoo Authenticator App on PC — Turn On 2-Step Verification

A Yahoo Mail inbox is where other services send their password-reset links, so whoever gets into it can take the accounts behind it too — and old Yahoo passwords are in many leaks. With 2-step verification on, Yahoo also asks for a code from your authenticator, so a leaked password alone no longer opens the inbox.

Turn on 2-step verification at Yahoo

Yahoo asks for at least two recovery methods on the account — such as a recovery phone number and email address — before you turn it on. If you sign in with Yahoo Account Key, turn Account Key off first: the two cannot be on at the same time.

Sign in to your Yahoo Account Security page on your computer.
Under “Ways of signing in”, click “2-step verification”.
Select “Authenticator app” and click “Continue”.
Yahoo shows a QR code. Leave it on the screen and add it to the extension as described below, then click “Continue”.
Enter the code from the extension and click “Done”.

Yahoo’s own instructions

Add Yahoo to Authenticator

Install 2FA Authenticator from the Chrome Web Store and pin it to the toolbar, so its icon is one click away.
Leave the Yahoo page with the QR code open. Click the Authenticator icon, then “Add Account” → “QR Code” → “Scan QR from screen”.
The account appears in the list with a six-digit code that changes every 30 seconds. Rename it if you like — the name is only for you.
Go back to Yahoo and type the current code into the confirmation field. If it is about to expire, wait for the next one.
Yahoo confirms that two-factor authentication is on. From now on it will ask for a code when you sign in — click the extension icon and copy it.

No QR code, or it will not scan? Look for the option to enter a key manually on Yahoo’s setup screen, copy the key, and add it in the extension with “Add Account” → “Manual” → “Secret Key”.

Get 2FA Authenticator for Chrome — free

Keep a way back into Yahoo

If Yahoo shows you a recovery code while you set up the authenticator, print it or write it down and keep it away from this computer. Beyond that, your way back is the recovery phone number and email address on the account — keep them current on the Account Security page — and the extension’s automatic backups.

The code is not accepted?

Almost always the computer’s clock. The codes are calculated from the current time, so a clock that is a minute off produces codes that look right and are refused. Turn on automatic date and time in your system settings — step-by-step for Windows, macOS and Linux.

If the clock is right, check the key itself: paste it into the TOTP code generator and compare the code with the one in the extension. If they differ, the key was copied wrong — add the account again.

Questions

Do I need the Yahoo app or Account Key for 2-step verification?: No. Yahoo offers prompts in its own apps, but also accepts codes from any authenticator app. The Authenticator extension reads the QR code straight off the Account Security page and generates the codes in Chrome. Account Key has to be off before 2-step verification can be turned on.
My mail app stopped signing in after I turned on 2-step verification.: Desktop mail programs such as Outlook or Apple Mail cannot ask for a code. On the Account Security page, generate an app password and enter it in the mail program instead of your normal Yahoo password.
What if I lose access to my authenticator?: Use the recovery code if Yahoo gave you one, or the recovery methods on the account, to get back in — then set the authenticator up again. That is why Yahoo asks for two recovery methods before you start, and why keeping the extension’s automatic backups on matters.
Why does Yahoo say my code is wrong?: Usually the computer clock is off by a minute or more. Turn on automatic date and time and try the next code. If it still fails, remove the account from the extension, turn 2-step verification off and on again, and add the new QR code.

Your codes, one click from the login page

Authenticator keeps your 2FA codes in the browser, on your device only — free, open source, no account and no phone needed. Local backups and optional password protection come built in.