snake_case converter

How snake_case works

snake_case joins multiple words into a single identifier using underscores as the separator, with every letter in lowercase. Examples: first_name, get_user_id, is_logged_in, parse_json_payload. The name comes from the low, flat visual rhythm the underscores create — it looks like a snake slithering along the baseline.

The all-uppercase sibling, SCREAMING_SNAKE_CASE (also called CONSTANT_CASE), uses the same separator but is reserved for constants and environment variables: MAX_RETRIES, DATABASE_URL. Mixing the two is a style smell — stick with lowercase snake for values that vary, screaming snake for values that don't.

This tool normalizes the input first — it splits on spaces, existing underscores, hyphens, dots, slashes, and case transitions — then rejoins with underscores and lowercases everything. Paste firstName, first-name, First Name, or FIRST_NAME and you'll get the same output: first_name.

When to use snake_case

snake_case is the right call when your language or data format calls for it:

• Python — PEP 8 mandates snake_case for variables, functions, methods, and module names.
• Ruby — method names, local variables, and symbols all use snake_case by convention.
• Rust — variables, functions, and module names. Types use PascalCase; constants use SCREAMING_SNAKE_CASE.
• PHP — function names in the PSR-12 standard, though class methods often drift toward camelCase.
• PostgreSQL / MySQL — table and column names. Using camelCase in SQL works but requires quoting identifiers in Postgres, which is friction.
• REST APIs — GitHub, Stripe (legacy fields), and most Python/Ruby-origin APIs use snake_case in JSON. Know your API before you guess.

Need the JavaScript-style variant or URL-style variant? camelCase converter and kebab-case converter use the same input parsing. For a deeper comparison of when each is appropriate, see camelCase vs snake_case.