The same identifier can be written as camelCase, PascalCase, or snake_case depending on the language or context you're in. This article covers the naming conventions you'll run into in code, which language or context each one conventionally belongs to, and why keeping them consistent matters.
Naming Conventions Commonly Used in Code
Taking the same concept — "user login count" — as an example, here's how it looks in each style:
- camelCase:
userLoginCount— the first word is lowercase, and every subsequent word is capitalized and joined with no separator. - PascalCase:
UserLoginCount— the same rule as camelCase, except the first word is capitalized too. - snake_case:
user_login_count— every word is lowercase, joined with underscores (_). - kebab-case:
user-login-count— like snake_case, but joined with hyphens (-) instead of underscores. - CONSTANT_CASE:
USER_LOGIN_COUNT— the same separator as snake_case, but every letter is uppercase.
The names differ, but the purpose is the same: express a multi-word concept as a single valid identifier (a variable name, filename, or URL — none of which can contain spaces) while still keeping the word boundaries visible.
Which Language or Context Uses Which
Each style has settled into being the convention for a specific language or context. JavaScript, Java, and C# use camelCase for variable and function names (e.g. getUserName) and PascalCase for class names (e.g. UserAccount). Python and Ruby go the other way for variables and functions, using snake_case (e.g. get_user_name), while still following PascalCase for class names. kebab-case is the de facto standard for CSS class names (.user-card), HTML attributes (data-user-id), and URL paths (/guides/case-styles/), because hyphens are treated more naturally than underscores in CSS and URL syntax. Finally, CONSTANT_CASE is used across languages whenever you want the naming itself to signal "this is a constant that doesn't change" (e.g. MAX_RETRY_COUNT, API_BASE_URL).
Why Consistency Matters
No single style is objectively better, but mixing them within one project causes real problems. If the same kind of value is written userId in one place and user_id in another, every reader has to stop and remember which spelling is used where, and autocomplete or search for the identifier becomes unreliable. Linters and formatters like ESLint and Prettier typically ship rules that enforce a single naming convention project-wide, because standardizing on one style reduces code review time and mistakes, not just improves readability. This matters even more in projects that span multiple languages — for example, an API response that maps a Python backend's snake_case field names to a JavaScript frontend's camelCase — where you need to know exactly where the convention switches to avoid bugs. One task that comes up constantly when standardizing naming is a plain uppercase/lowercase conversion. For example, turning user_login_count (which already has its words separated by underscores) into CONSTANT_CASE only requires uppercasing the whole string — and that kind of case conversion can be handled instantly with a text tool.
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camelCase, snake_case & Other Naming Conventions — When to use each naming style