Why use a password manager? Because it's one of the best apps you can invest in, saving you time and protecting all the accounts you need a password for. A good password manager generates and stores passwords and makes it easy to change them. Many managers offer other features, like filling in your information in online forms. However, not every password manager is worth its weight in code. To be truly useful, a password manager must provide good password generation, industry-standard AES-256 encryption (and ideally two-factor authentication), autofill options, and cross-platform compatibility.

Password generation

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RoboForm Everywhere helps you generate stronger passwords.

Most password managers create passwords, knowing that most of us aren't coming up with excellent ones on our own. We tend to choose passwords we can readily recall, such as pet names, birthdays, cities we're from -- information that's easily discovered online, especially on social media. (For tips on making stronger passwords, see Passwords 101.) Moreover, we reuse our passwords, so a hacker who figures out one password can unlock multiple accounts.

A good password manager runs a diagnostic of your current passwords and switches them to more complex passwords, a unique one for each account. Dashlane, LastPass, and 1Password do this well. You needn't worry about remembering all of them, only your single master password.

If one of the sites where you have an account is ever compromised, a good password manager alerts you and offers to generate a new password, just in case hackers have acquired your current one. Dashlane, LastPass, 1Password, and McAfee LiveSafe all provide this service.

Encryption

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1Password offers AES-256 encryption.

A password manager should encrypt your log-in emails and passwords. The Advanced Encryption Standard (AES) is the specification established by the US National Institute of Standards and Technology -- it's the encryption used for classified documents, but the standard is used worldwide. The strongest level of AES is 256-bit, so look for that when checking a password manager's features. Dashlane, Blur, LastPass, Sticky Password, SafeInCloud, LoginBox Pro, My Passwords, and Password Safe Pro all offer this military-grade encryption.

You should investigate how the password manager handles encryption. Ideally, your data should be encrypted and decrypted locally on your device, so that this info isn't stored elsewhere. Dashlane, LastPass, RoboForm, Sticky Password, Keeper, 1Password, mSecure Password Manager, and OneSafe all offer this.

Many password managers are adding two-factor authentication, which requires an additional step to log in. For example, after you enter your password, you're asked for a code that the app has texted to you. Dashlane, LastPass, RoboForm, Keeper, mSecure Password Manager, OneSafe, McAfee LiveSafe, SafeInCloud, Norton Identity Safe, and LoginBox Pro all offer this added layer of protection.

Autofill

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Keeper autofills log-ins, forms, and more for you.

After you enter your master password (and perhaps a second authentication factor), your password manager shouldn't require any other input. You should be able to access your accounts simply by clicking to launch them.

Some password managers go a step further, storing your basic personal information -- name, address, phone number, birth date -- in an encrypted file. With this feature, you can autofill online forms with just one click. Online shoppers should feel confident storing their credit card and shipping info to expedite the ordering process. All major apps offer this feature, except for Android password managers.

Cross-platform access

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Sticky Password works well across all platforms.

Most of us rely on multiple devices -- home and work computers, phones, tablets -- and expect to work fluidly across them. A good password manager is cross-platform, putting your sensitive log-ins and other data at your fingertips no matter where you're logging in from. All the major apps we tested offer this except for OneSafe, which doesn't include Windows, and Norton Security, which has a separate app for iOS. Dashlane, Blur, LastPass, Sticky Password Premium, RoboForm, and mSecure have a four-for-one premium price. Keeper, 1Password, and OneSafe let you choose to pay for one device, a bundle of two, or all of them.

A good password manager also includes plug-ins for the major Web browsers (Chrome, Firefox, Safari, Opera, and Internet Explorer). With those, you can access your password manager from any computer without having to download another app. Of all the password managers we tested, only mSecure doesn't offer this capability.

More password resources

Joshua Rotter is a copy editor for Download.com and covers iOS.