Case Converter: camelCase, snake_case, UPPER & More

Most languages and tools have a preferred way to join words in an identifier. JavaScript and Java use camelCase for variables and functions, and PascalCase for classes and React components. Python and Ruby favor snake_case, while CONSTANT_CASE (or SCREAMING_SNAKE_CASE) marks constants and environment variables. kebab-case is the norm for URLs, CSS classes, CLI flags and npm package names. Train-Case shows up in HTTP header names like Content-Type. dot.case and path/case are handy for config keys, i18n message IDs and file paths.

To convert case from one style to another, you have to solve one problem first: finding the word boundaries. This tool breaks the input apart in three ways. It splits where a lowercase letter or digit is followed by a capital, so userId becomes user and id. It separates a run of capitals from the word that follows, so HTMLParser becomes HTML and Parser rather than one long word. And it treats any character that isn't a letter or digit, including spaces, underscores, hyphens, dots and slashes, as a separator. The resulting words are lowercased, then rejoined in each target style.

A few things to know about that approach. Acronyms are normalized, so parseHTML becomes parse_html in snake_case and ParseHtml in PascalCase. In the identifier styles, punctuation is dropped rather than carried over, which is what you want for variable and file names, and only ASCII letters and digits count as word characters, so accented letters act as separators there. The four prose styles work differently: UPPERCASE, lowercase, Title Case and Sentence case only change letter case, so punctuation, spacing and accented letters like é stay exactly as you typed them. That makes the page a plain uppercase converter or lowercase converter for normal sentences too. Title Case capitalizes every word and doesn't apply style-guide rules for short words like "of" or "the".

Because every format is shown at once, this text case converter is also a quick way to rename something consistently across layers, such as a database column, an API field and a TypeScript property.