camelCase, snake_case, kebab-case and Title Case: Which Goes Where

Case conventions look like style, but at the edges between systems they decide whether code works. A column called userId behaves differently from user_id in PostgreSQL, a URL with underscores is read differently from one with hyphens, and converting XMLHttpRequest to snake_case can go wrong in more than one way. This guide covers where each convention is expected and what automatic conversion does to awkward names.

Who expects what

The rule that holds everywhere: pick the convention of the system you're writing for, and convert at the boundary. A Python backend can use created_at internally and still serve createdAt to a JavaScript client, as long as one layer does the translation consistently.

Why camelCase column names hurt in PostgreSQL

PostgreSQL folds unquoted identifiers to lowercase. Create a column as "userId" (with quotes, as some ORMs do) and a hand-written query SELECT userId FROM users looks for userid and fails with column "userid" does not exist. From then on you have to quote the name every time: SELECT "userId" FROM users. A user_id column never needs quotes, which is why snake_case is the safe default for SQL even when the application code around it is camelCase.

What automatic conversion does to awkward names

A converter has to decide where words start. The Text Case Converter splits at spaces, punctuation, underscores and hyphens, between a lowercase letter or digit and a capital, and between an acronym and the word after it. Here is what that produces for names that trip converters up:

Three patterns to watch:

• Acronyms lose their capitals. In camelCase output an acronym becomes an ordinary word (xmlHttpRequest, orderTotalInr). Google's Java and JavaScript style guides actually prefer this form (XmlHttpRequest, not XMLHTTPRequest), but if your codebase keeps acronyms in capitals, fix them by hand.
• Brand names split in the wrong place. iPhone becomes i_phone, because a capital after a lowercase letter looks like a word boundary. There is no rule that can tell iPhone from userName, so check proper nouns.
• Title Case is for prose. It capitalises each run of letters and doesn't split joined identifiers, so XMLHttpRequest becomes one word. Convert an identifier to snake_case first if you want "Xml Http Request" style words.

Title Case and sentence case

For headings, Title Case capitalises the first letter of each word, and sentence case capitalises only the first word and proper nouns. The converter's Title Case capitalises every word, including short ones, and lowercases the rest of each word: "the lord of the rings" becomes "The Lord Of The Rings", "NASA" becomes "Nasa" and "O'Brien" becomes "O'brien". Style guides such as AP and Chicago keep short words like "of" and "the" in lowercase unless they start the title, so a heading usually needs a quick manual pass after conversion.

Slugs are a separate job

A URL slug needs more than kebab-case: accented letters simplified, punctuation removed, and repeated separators collapsed. The Slug Generator does that, so "Crème Brûlée à São Paulo" becomes creme-brulee-a-sao-paulo, while the case converter keeps the accents.