Case Sensitivity in URLs, Emails and Passwords

Some systems treat "A" and "a" as the same character; others treat them as completely different. Knowing which is which prevents broken links, failed logins and lost emails.

Passwords: always case-sensitive

"Sunset" and "sunset" are different passwords. That is why using both uppercase and lowercase letters increases the number of possible combinations, and why Caps Lock warnings exist on login screens.

URLs: partly case-sensitive

• Domain names are not case-sensitive. EXAMPLE.COM and example.com are the same.
• Paths may be case-sensitive. On many Linux web servers, /About.html and /about.html are different files. Windows servers are usually case-insensitive.

Mixed-case URLs can create broken links and duplicate content. This is why lowercase URL slugs are recommended; our slug generator lowercases by default.

Email addresses: mostly not

The domain part (after @) is not case-sensitive. Technically the local part (before @) can be, but almost all email providers treat it as case-insensitive. Store and compare emails in lowercase in your applications to avoid duplicate accounts.

Usernames and hashtags

Most platforms treat usernames as case-insensitive. Hashtags generally are too, but writing them in CamelCase, as in #ThrowbackThursday, makes them easier to read and helps screen readers pronounce each word.

File names

Windows and default macOS file systems ignore case for file names, but Linux does not. A website built on Windows may break when uploaded to a Linux host if links do not match the file names exactly. Using lowercase file names everywhere avoids the problem.

Programming

Most programming languages are case-sensitive: userName and username are different variables. Consistent naming conventions, applied with a case converter if needed, prevent subtle bugs.

Frequently asked questions

Are URLs case sensitive?

Are URLs case sensitive? The domain is not, but the path can be on many servers. That is why lowercase URLs are recommended.

Are email addresses case sensitive?

Are email addresses case sensitive? In practice, no; providers treat them as case-insensitive. Store lowercase email addresses in your database and use case-insensitive comparison when users log in.

Are passwords case sensitive?

Are passwords case sensitive? Yes, always. "Sunset" and "sunset" are different passwords, which is why mixing upper and lower case adds strength.