What is snake_case?

snake_case is a naming convention where multi-word identifiers are written in all lowercase with words separated by underscores. For example, "user first name" becomes "user_first_name". It is one of the most readable naming conventions because the underscores act as clear visual separators between words.

Where is snake_case used?

snake_case is the standard naming convention in Python (PEP 8), Ruby, Rust, and PostgreSQL. It is also common for database column names, environment variables (often in SCREAMING_SNAKE_CASE), and REST API field names in Python-based frameworks like Django and FastAPI. C and C++ also traditionally use snake_case.

// JavaScript — convert camelCase to snake_case
function toSnakeCase(str) {
  return str
    .replace(/([A-Z])/g, '_$1')
    .toLowerCase()
    .replace(/^_/, '');
}
toSnakeCase('userFirstName');  // 'user_first_name'

# Python — convert camelCase to snake_case
import re
def to_snake_case(s):
    return re.sub(r'(?<!^)(?=[A-Z])', '_', s).lower()
to_snake_case('userFirstName')  # 'user_first_name'