camelCase to snake_case Converter

camelCase joins words by capitalizing each new word (userFirstName). snake_case writes the words in lowercase and puts an underscore between them (user_first_name). The same name often has to move between the two: a JavaScript object property becomes a database column, a JSON field becomes a Python variable, or an API response is mapped to another language's conventions. This page converts a list of names in one step, one name per line.

Each line is split into words at spaces, hyphens, underscores and at every boundary where a lowercase letter or number is followed by a capital letter. The words are then written in lowercase and joined with underscores. PascalCase names such as UserFirstName work the same way, and the other buttons give kebab-case, CONSTANT_CASE and the reverse direction.

Because only the lowercase-to-capital boundary is detected, a run of capitals stays in one word. XMLHttpRequest becomes xmlhttp_request and getHTTPResponse becomes get_httpresponse. If your names contain acronyms, fix those few by hand.

Python, Ruby and Rust conventionally use snake_case for variables and functions, and SQL column names are often snake_case too. JavaScript, Java and Swift prefer camelCase for variables and methods. When data crosses between these worlds, converting names mechanically avoids typing mistakes, but always check the result against your schema before you use it.