Case Converter

A case converter changes the capitalisation of text, switching between UPPERCASE, lowercase, Title Case, Sentence case and programming styles such as camelCase and snake_case.

It is a quick tool for writers, editors and developers who need to reformat text without retyping it.

Upper and lower case are mechanical transformations with one right answer. Title case is not. It depends on which style guide you follow, and the guides genuinely disagree about which words to capitalise.

The common thread is that major words are capitalised and minor ones are not, but the definition of minor varies. Some guides lower-case all prepositions; others capitalise those of four or more letters, so "Between" is capitalised under one and not the other. Most agree that the first and last words are capitalised regardless of what they are.

• Articles (a, an, the) and short conjunctions (and, but, or) are lower-cased by essentially every guide.
• Hyphenated compounds and the word after a colon are handled differently between guides.
• Any automated title case applies one convention. Check the output against whichever guide the document follows rather than assuming.

Changing case looks like a character-by-character operation and is not, because the correct mapping depends on the language the text is in. The same input can correctly produce different output under different locales.

Turkish is the standard example: it distinguishes dotted and dotless i, so upper-casing "i" gives "İ" in Turkish and "I" in English, and lower-casing "I" reverses the problem. German ß has historically upper-cased to "SS", which changes the length of the string. Neither behaviour is a bug.

• Some characters change length when case is changed, so upper-casing is not always a one-to-one mapping.
• Comparing strings case-insensitively across languages requires case folding rather than simple lower-casing.
• Identifiers, filenames and code should be case-converted with an invariant locale, so behaviour does not change with the user's system settings.