snake_case Converter — Rules, Use Cases & Examples

What is snake_case?

snake_case is a naming convention where all words are lowercased and joined by underscores. There are no spaces, no capital letters, and no other separators. The name is a visual metaphor: the underscores resemble a snake lying flat on the ground.

Typical snake_case identifiers:

• user_profile — a variable or table name
• get_user_name — a function name in Python
• total_item_count — a counter variable
• created_at — a database column name
• max_retry_attempts — a configuration value

The rules are simple: lowercase every letter, replace every space or punctuation boundary with an underscore, and remove everything else.

Where snake_case is the standard

snake_case is not universal — it is the dominant style in specific ecosystems.

• Python: PEP 8 mandates snake_case for all variable names, function names, method names and module (file) names. Class names use PascalCase; constants use SCREAMING_SNAKE_CASE.
• SQL: Column names, table names and stored procedure names are conventionally written in snake_case across PostgreSQL, MySQL and most SQL dialects. SQL identifiers are case-insensitive, but snake_case is unambiguous across tools and editors.
• Ruby: snake_case is idiomatic for method names and local variables. Rubocop, the Ruby linter, enforces this by default.
• Rust: The compiler issues warnings for non-snake_case variable and function names. Only types and traits use PascalCase.
• File names: snake_case is safe for file names on all operating systems because underscores are unambiguous. Spaces cause problems in shell scripts; hyphens are treated as operators in some contexts.
• REST API JSON keys: Many REST APIs (particularly those designed by Python or Ruby teams) return JSON with snake_case keys: first_name, created_at, account_id.

snake_case vs kebab-case

Both snake_case and kebab-case use lowercase words — the only difference is the separator character. snake_case uses underscores (_); kebab-case uses hyphens (-). The choice of separator is determined by where the identifier will be used:

• In code (Python, SQL, Rust): use snake_case. Hyphens are not valid in most programming language identifiers because the parser interprets them as the subtraction operator.
• In HTML/CSS: use kebab-case. CSS class names like btn-primary and HTML data attributes like data-user-id follow this convention by specification.
• In URLs: use kebab-case. Google recommends hyphens over underscores in URL paths for better SEO, as Google's crawler historically treated underscores as word-joiners rather than word-separators.

SCREAMING_SNAKE_CASE — the constant variant

SCREAMING_SNAKE_CASE (also called CONSTANT_CASE or UPPER_SNAKE_CASE) follows the same separator rule as snake_case but uppercases every letter. It signals to the reader that an identifier is a constant — a value that never changes at runtime.

• MAX_CONNECTIONS — a database pool limit
• API_BASE_URL — a configuration endpoint
• DEFAULT_TIMEOUT_MS — a timing constant
• HTTP_STATUS_OK — a status code alias

In Python this is used for module-level constants. In JavaScript it is used for const values that represent fixed configuration or magic numbers. In Java and C it is the standard for static final and #define values respectively.

Frequently asked questions