Snake Case Converter

How to use the snake case converter

1. Paste or type your names in Your text, one per line. Click Example to load a sample, or Open file to read a .txt or .csv file.
2. Under Style, choose snake_case for lowercase names or SCREAMING_SNAKE_CASE for capitals.
3. The Result box updates as you type. Each input line gives one output line.
4. Click Copy or Download .txt, or continue with the result in the camelCase, kebab-case or slug tools.

The two styles

Both styles split the text into the same words; only the letter case differs. Which one to use depends on the convention of your language or project. Python’s style guide, PEP 8, asks for lowercase with underscores for function, variable and method names and for capitals with underscores for module-level constants such as MAX_OVERFLOW. The Rust API Guidelines use snake_case for modules, functions, methods, macros and local variables, and SCREAMING_SNAKE_CASE for constants and statics.

How the converter finds the words

Each line is split into words, then the words are lowercased (or uppercased) and joined with single underscores. A new word starts:

• At any character that is not a letter or digit: spaces, tabs, hyphens, dots, slashes, commas, brackets and existing underscores. Several in a row count as one break, and breaks at the start or end of a line are dropped, except underscores: leading and trailing underscores are kept, so _private_var and __init__ stay as they are.
• Not at an apostrophe inside a word: straight and curly apostrophes between letters are removed, so don't stop becomes dont_stop and user’s name becomes users_name.
• Where a lowercase letter or digit is followed by a capital: firstName → first, Name; version2Beta → version2, Beta.
• Before the last capital of a run of capitals followed by a lowercase letter: HTTPResponse → HTTP, Response. That is how acronyms stay in one piece.

Digits stay attached to the letters before them, so utf8Encode becomes utf8_encode and base64Encode becomes base64_encode. Text that is already in snake_case passes through unchanged, and SCREAMING_SNAKE_CASE input such as API_KEY simply becomes api_key.

Edge cases to check by hand

The rules above work for most real names, but a few inputs give results you may want to edit:

Letters from any alphabet are kept, accents included: café au lait becomes café_au_lait and ДобрыйДень becomes добрый_день. If your database or language only accepts ASCII names, run the text through Remove accents first. In SCREAMING_SNAKE_CASE the German ß becomes SS (straße → STRASSE), which is the standard uppercase form.

Line breaks are kept and Windows line endings are written as plain line feeds. A line that contains only spaces or punctuation becomes an empty line, so the output always has as many lines as the input.

When people need snake_case

• Database columns. Spreadsheet headers such as Email Address or Total Revenue (USD) become email_address and total_revenue_usd, ready for a CREATE TABLE statement. In PostgreSQL this also avoids quoting: unquoted identifiers are folded to lowercase, so a column created as "FirstName" must be quoted in every query, while first_name never needs quotes.
• Moving code between languages. A JavaScript or Java API returns createdAt and userId; a Python model expects created_at and user_id. Paste the field list, one per line, and copy the result.
• Environment variables and constants. Switch to SCREAMING_SNAKE_CASE to turn database url or apiKey into DATABASE_URL and API_KEY.
• File names and keys. Translation keys, analytics event names and file names often use snake_case because it contains no spaces and reads well.

For a list that arrives on one line, separated by commas, split it into lines first: first name, last name, email on one line becomes a single name, first_name_last_name_email. The comma separator can turn a comma list into lines and back.

snake_case, camelCase and kebab-case

All three cases join the same words; they differ in the separator and in capitals. snake_case uses underscores and lowercase, camelCase removes the separators and capitalizes every word after the first, and kebab-case uses hyphens. Hyphens are not allowed in most programming identifiers because they read as a minus sign, which is why kebab-case is used for CSS classes and URLs rather than variables. The guide camelCase vs snake_case vs kebab-case compares where each is used.

One thing does not survive a round trip: snake_case does not record which words were acronyms. HTTPResponseCode becomes http_response_code, and converting that back with the camelCase converter gives httpResponseCode, not the original. Keep the original names if you need them later.

Questions