Convert case

Which rule each case applies

Title case and Sentence case treat the capitals you already typed in opposite ways, and that is the thing that catches people out. Title case leaves any word carrying a capital after its first letter exactly as written — iPhone, NASA, McDonald — and only makes decisions about the rest. Sentence case lowercases the whole passage first and then capitalises after each full stop, question mark, exclamation mark or ellipsis, so NASA becomes Nasa and no list of exceptions protects it. Sentence case has no abbreviation rule either, so "e.g. this" gains a capital where the word counter on this site would not have split the sentence at all. For a passage full of acronyms, Title case is the safe one and Sentence case needs reading afterwards.

The default language setting is no language. Upper and lower use the browser's plain rules unless you pick Turkish, Azeri, Lithuanian or Greek from the list, so Turkish text converted on the default setting comes out with English's dotted and dotless i — the page notices a dotless ı or a dotted İ in what you pasted and says so rather than letting it through in silence. The warning about German ß becoming SS covers UPPERCASE and CONSTANT_CASE, which are the two you are most likely to want; the alternating and inverted cases also capitalise it, and do not warn.

Title case decides word by word on whitespace alone, so anything joined by a hyphen or a slash counts as one word and receives one capital: "mother-in-law" stays "Mother-in-law". The programmer cases split on something else entirely — capitals, digits, spaces, underscores, hyphens, dots and slashes — with the extra rule that keeps a run of capitals together, which is what makes XMLHttpRequest into xml_http_request rather than xmlhttp_request. Converting a list line by line splits on line feeds only, so a carriage return from a Windows file stays attached to the end of each line and travels into the result with it.

When you want something else

Anything that has to be reversible should not be uppercased at all. There is no way back from SS to ß, from an accentless Greek capital to the accented original, or from a name list whose internal capitals you needed — the information is gone rather than hidden, so keep the original alongside whatever you convert. That is not a limitation of this page; it is what casing is.

For a file rather than a paste, the obvious command-line answers are the trap. tr and awk's toupper are ASCII-only: they will uppercase the English letters in a name list and leave every accented one untouched, which corrupts the list quietly and looks like it worked. A Python or Node one-liner does the Unicode-correct thing instead, and for Turkish, Azeri, Lithuanian or Greek you need a call that takes a locale — the same four this page offers, for the same reason. Renaming a folder of files to lower case is a different job again, and one where a case-insensitive filesystem, which is the default on macOS and Windows, will treat README and readme as the same name.