camelCase vs snake_case: Which Naming Convention Should You Use?
A developer’s guide to choosing the right naming convention for every context.
Naming conventions are one of the first things every developer has to decide on, and one of the most common sources of style debates in code reviews. The two heavyweights are camelCase and snake_case, but PascalCase, kebab-case, and SCREAMING_SNAKE_CASE all have important roles depending on your language, framework, and file type. This guide breaks down when and where to use each.
The Five Major Conventions
Before diving into language-specific rules, here is a quick reference for the five naming conventions you will encounter most often in professional codebases:
| Convention | Example | Primary Use |
|---|---|---|
| camelCase | getUserName | Variables, functions (JS, Java, Swift) |
| PascalCase | UserProfile | Classes, components, types |
| snake_case | user_name | Variables, functions (Python, Ruby, Rust) |
| SCREAMING_SNAKE_CASE | MAX_RETRIES | Constants, env vars (all languages) |
| kebab-case | user-profile | URLs, CSS classes, filenames |
Language-by-Language Guide
JavaScript and TypeScript
JavaScript uses camelCase for variables, functions, and object properties. PascalCase is reserved for classes, React components, and TypeScript interfaces or type aliases. Constants typically use SCREAMING_SNAKE_CASE, though some teams use camelCase for non-primitive constants. File names for React components follow PascalCase (UserProfile.tsx), while utility files use kebab-case (format-date.ts).
Python
Python’s PEP 8 style guide is clear: snake_case for variables, functions, and module names. PascalCase for class names. SCREAMING_SNAKE_CASE for constants. Python is one of the most consistent ecosystems when it comes to naming — deviating from PEP 8 in a Python project will draw immediate attention in code review.
Java
Java uses camelCase for variables and methods, PascalCase for class and interface names, and SCREAMING_SNAKE_CASE for static final constants. Package names are all lowercase with dots as separators (com.example.myapp). The Java ecosystem is mature enough that these conventions are nearly universal.
Go
Go uses camelCase for unexported (private) identifiers and PascalCase for exported (public) identifiers. This is not just a convention — it is enforced by the language itself. If a function starts with an uppercase letter, it is accessible from other packages. This makes Go unique in that casing has semantic meaning beyond readability.
Ruby
Ruby follows snake_case for methods and variables, PascalCase (which Ruby calls “CamelCase”) for classes and modules, and SCREAMING_SNAKE_CASE for constants. Filenames use snake_case. The Ruby community strongly enforces these conventions through tools like RuboCop.
Rust
Rust uses snake_case for functions, variables, modules, and file names. PascalCase is used for types, traits, and enum variants. SCREAMING_SNAKE_CASE is for constants and statics. Rust’s compiler actually emits warnings if you violate these conventions, making it one of the strictest languages on naming.
CSS
CSS class names and custom properties use kebab-case. This is so universal that it barely needs stating, but it is worth noting that CSS-in-JS libraries like styled-components and Emotion often convert to camelCase for JavaScript compatibility. If you are writing BEM-style CSS, you will see patterns like block__element--modifier which extend kebab-case with double underscores and double hyphens.
When Conventions Collide
The trickiest situations arise at the boundaries between ecosystems. A REST API might return JSON with snake_case keys (because the backend is Python) but the JavaScript frontend expects camelCase. Common solutions include writing a transformation layer that converts keys at the API boundary, or adopting camelCase in the API contract regardless of the backend language.
Database columns are almost always snake_case, even when the application code uses camelCase. ORMs like Sequelize, SQLAlchemy, and ActiveRecord handle the mapping between user_name in the database and userName in the application code.
Readability Research
A 2010 study by Binkley et al. published in Empirical Software Engineering found that camelCase identifiers are recognized more quickly by experienced programmers, while snake_case identifiers are recognized more quickly by novices. The difference was statistically significant but small in absolute terms. The practical takeaway is that familiarity matters more than any inherent readability advantage — follow the convention your team and language already use.
The Bottom Line
The best naming convention is the one your language and team already use. Consistency within a codebase matters far more than any theoretical advantage of one format over another. If you are starting a new project, follow the official style guide for your language. If you are joining an existing project, match what is already there. The worst outcome is a codebase where some files use camelCase and others use snake_case with no discernible pattern.
Need to convert between naming conventions? Our free case converter tool supports camelCase, PascalCase, snake_case, SCREAMING_SNAKE_CASE, kebab-case, and more — all processed locally in your browser.