Everyone has typed a whole paragraph with caps lock on. Fixing it by retyping is a waste of an afternoon, and this tool does it in a blink. Paste the text above and everything becomes lowercase.
That covers the obvious job. Lowercase is also a quiet workhorse for data, because most computers treat “Paris”, “PARIS” and “paris” as three different strings, and you rarely want that.
Where lowercase helps with data
Email addresses are effectively case-insensitive, and putting a list in one case before you remove duplicates stops “Jane@Example.com” and “jane@example.com” counting as two people. The same goes for hashtags, tags, categories and usernames. URL paths and file names are far less trouble when everything is lowercase, since some servers treat Page.html and page.html as different files. If you are building web addresses, the slug generator lowercases for you and also removes the characters that do not belong in a URL.
Keyword lists benefit too. Before counting words in the word frequency counter, lowercasing makes “Free” and “free” the same word, although that tool has a case switch of its own.
Fixing text typed in caps
When the only problem is caps lock, plain lowercase leaves you with no capitals at all. The tool for that is sentence case, which lowercases everything and then puts a capital back at the start of each sentence. You will still need to restore the names of people and places by hand, and the word “I”, since no tool can know which words are names. For headlines, title case is the right next step.
Details worth knowing
Accented letters keep their accents, so É becomes é. Greek and Cyrillic work as well, and the Greek capital sigma becomes the right form at the end of a word, ς, instead of the middle-of-word σ. Characters with no lowercase form, like digits, punctuation, emoji and Chinese or Japanese text, are unchanged.
A rare quirk: the Turkish capital dotted İ becomes “i” followed by a separate combining dot, which looks right on screen but is two characters long. It will only matter if you use that letter and then compare strings.
Line breaks and spacing are untouched, so lists keep their shape. If you want to go the other way, there is the uppercase converter, and the case converter shows eleven styles at once.
Case sensitivity in practice
Whether “Report.pdf” and “report.pdf” are the same file depends on the system. Linux file systems treat them as different files. Windows and macOS usually keep the capitals you typed but treat the two names as the same file, which causes confusing problems when a project moves between them: a link that works on your laptop returns “not found” on a Linux server. That is one more reason to keep file names and URLs in lowercase. Git on a case-insensitive system can also lose track of a rename that only changes capitals, so changing “Readme” to “README” sometimes needs two steps.