What Does Case Sensitive Mean?

Definition of Case Sensitive, Case Sensitive Passwords, & More

Picture of a collection of antique wooden letters
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Anything that is case sensitive discriminates between uppercase and lowercase letters. In other words, it means that two words that appear or sound identical, but are using different letter cases, are not considered equal.

For example, if a password field is case sensitive, then you must enter each letter case as you did when the password was created. Any tool that supports text input might support case sensitive input.

Where Is Case Sensitivity Used?

Examples of computer related data that is oftentimes, but not always, case sensitive include commands, usernames, file names, variables, and passwords.

For example, because Windows passwords are case sensitive, the password HappyApple$ is only valid if it's entered in that exact way. You can not use HAPPYAPPLE$ or even happyApple$, where just a single letter is in the wrong case. Since every letter can be uppercase or lowercase, each version of the password that uses either case is really an entirely different password.

Email passwords are often case sensitive, too. So, if you're logging into something like your Google or Microsoft account, you must be sure to enter the password in exactly the same way you did when it was created.

Of course, these aren't the only areas where text can be distinguished by letter case. Some programs that offer a search utility, like the Notepad++ text editor and the Firefox web browser, have an option to run case sensitive searches so that only words of the proper case entered into the search box will be found. Everything is a free search tool for your computer that supports case sensitive searches, too.

Screenshot of the Match Case option in a Firefox search
Firefox's 'Match Case' Find Option.

When you're making a user account for the first time, or are logging into that account, you may find a note somewhere around the password field that explicitly says the password is case sensitive, in which case it does matter how you enter the letter cases to login.

However, if a command, program, website, etc. does not discriminate between uppercase and lowercase letters, it could be referred to as case insensitive or case independent, but will probably not even mention it if so.

Security Behind Case Sensitive Passwords

A password that must be entered with the proper letter cases is much more secure than one that doesn't, so most user accounts are case sensitive.

Using the example from above, you can see that even those two incorrect passwords alone provide three total passwords someone would have to guess to get access to the Windows account. Plus, because that strong password has a special character and several letters, all of which could be uppercase or lowercase, finding the right combination wouldn't be quick or easy.

Imagine something simpler, though, like the password HOME. Someone would have to try all combinations of that password in order to land on the word with all the letters capitalized. They'd have to try HOMe, HOme, Home, home, hoMe, HoMe, hOme, etc.—you get the idea. If this password was case insensitive, though, every one of those attempts would work, plus, a simple dictionary attack would reach this password rather easily once the word home was tried.

With every additional letter added to a case sensitive password, the likelihood that it can be guessed within a reasonable amount of time is drastically reduced, and the security is amplified even more when special characters are included.

Tips and More Information

Because most passwords are case sensitive, the letter case you used is one of the first things to look at if your password is said to be wrong when trying to log in to a website. However, since most passwords are hidden behind asterisks, making it impossible to see whether you used the letter casing inappropriately, just check that the Caps Lock isn't enabled on your keyboard.

The Windows Command Prompt is case insensitive, meaning that you can enter commands like dir as DIR, DiR, dIr, etc.—there really isn't any reason to do that but if you happen to have typed it incorrectly, you don't have to worry about fixing it for the command to work.

Screenshot of Windows commands showing case insensitivity
Examples of Case Sensitivity With Windows Commands.

The same is true when referring to folder paths from the command line in Windows. For example, cd downloads is the same as cd Downloads.

Screenshot of an example of a case sensitive Linux command
Example of Case Sensitivity With a Linux Command.

Linux commands, however, are case sensitive. You have to enter them exactly as they appear or you'll get an error. Entering cd downloads when the folder is actually spelled "Downloads," will result in an error like "No such file or directory." Commands entered in the wrong case will return a "command not found" error.