Every format, with an example
Sentence case and Title Case: first letter up, rest down, The quick brown fox. Or principal words up and small words down, The Art of War. Capitalize Each Word skips the exceptions: The Art Of War.
camelCase: no separator, first word lowercase, myVariableName. Variables and methods in JavaScript, TypeScript, Java, Kotlin, Swift and C#.
PascalCase: the same with the first word capitalized, MyVariableName. Classes, types, React components, exported Go identifiers.
snake_case: my_variable_name. Python under PEP 8, Ruby, Rust, and almost every database column.
kebab-case: my-variable-name. URLs and slugs, CSS class names, HTML attributes, npm packages, CLI flags. In most languages it cannot be an identifier at all, since the hyphen reads as a minus sign.
CONSTANT_CASE: MY_VARIABLE_NAME. Constants and environment variables. SCREAMING_SNAKE_CASE is the same thing with a better name.
dot.case: my.variable.name. Config keys and log fields.
The acronym trap
getHTTPResponse or getHttpResponse? Google's style guides say treat an acronym as an ordinary word: lowercase it, then capitalize the first letter. That gives getHttpResponse and xmlHttpRequest, and Google's C++ guide writes StartRpc() rather than StartRPC(). Airbnb and Microsoft land in the same place.
Adjacent capitals erase the word boundaries, so parseHTTPURL is hard to read. This is the one spot where converters openly disagree with each other, mine included, so check acronyms in the output before committing them.
Does the convention matter
Consistency inside a project beats the choice itself. The split came from history: C settled on snake_case in the terminal era, Java brought camelCase in with its method names. An eye-tracking study by Binkley et al. put camelCase slightly ahead for experienced developers and snake_case for beginners, with the gap under 5%.
Prose has firmer rules. AP style keeps articles, conjunctions and short prepositions lowercase and capitalizes everything else. For most work: sentence case for body text, title case for headings.
On a Mac you pick a case once in Klipto's paste preview and it applies on ⌘V in any app. The case chips are exclusive there, so choosing snake_case replaces camelCase instead of stacking on top of it.