camelCase, snake_case, kebab-case — what are they and when to use each

If you have ever worked on a codebase with multiple people, you have probably seen the same concept written as userName, user_name, and user-name all in the same project. These are not typos — they are different naming conventions, each with its own rules, history, and appropriate context. Understanding them makes you a better developer and a more consistent writer.

Why naming conventions exist

Code and file names cannot contain spaces. When a concept naturally consists of multiple words — like "background colour" or "maximum retry count" — you need a way to join them without spaces while keeping the result readable. Naming conventions solve this problem, and different programming languages, frameworks, and communities have settled on different solutions.

Consistency within a codebase matters more than which convention you pick. A team that uses snake_case everywhere is far easier to work with than one that mixes styles inconsistently.

The main case styles explained

Style	Example	Rule
UPPERCASE	BACKGROUND_COLOR	All letters capitalised
lowercase	backgroundcolor	All letters lowercase
Title Case	Background Color	First letter of each word capitalised
Sentence case	Background color	Only the first letter capitalised
camelCase	backgroundColor	First word lowercase, subsequent words capitalised
PascalCase	BackgroundColor	Every word starts with a capital letter
snake_case	background_color	Words joined by underscores, all lowercase
kebab-case	background-color	Words joined by hyphens, all lowercase

camelCase

Named after the humps of a camel — the capital letters mid-word resemble a camel's silhouette. The first word is entirely lowercase; every subsequent word starts with a capital letter. No separators are used.

Where it is used:

• JavaScript and TypeScript variable and function names: getUserData(), isLoggedIn
• Java variable and method names
• JSON keys by convention
• Swift and Kotlin variables

PascalCase

Also called UpperCamelCase — identical to camelCase except the very first letter is also capitalised. Every word, including the first, starts with a capital.

Where it is used:

• Class names in almost every language: UserAccount, DatabaseConnection
• React components: NavBar, ProductCard
• C# variables and methods
• TypeScript interfaces and types

snake_case

Words are separated by underscores and everything is lowercase. It is easy to read because the underscore acts as a visible space — your eye naturally separates the words.

Where it is used:

• Python variables, functions, and file names: get_user_data(), max_retry_count
• Ruby variables and methods
• Database column names: created_at, user_id
• Constants in many languages (often UPPER_SNAKE_CASE): MAX_CONNECTIONS

kebab-case

Words are separated by hyphens. The name is a joke — the words are "skewered" together like kebab meat on a stick. Also called spinal-case or hyphen-case.

Where it is used:

• CSS class names and custom properties: background-color, font-size
• HTML attributes
• URL slugs: how-to-create-strong-password
• File names in web projects: user-profile.html
• npm package names: react-router-dom

Note: kebab-case cannot be used for variable names in most programming languages because the hyphen is interpreted as a minus operator.

UPPERCASE and constants

All-caps is reserved almost universally for constants — values that never change during program execution. The convention signals to any developer reading the code: "do not reassign this."

• MAX_RETRIES = 3
• API_BASE_URL = "https://api.example.com"
• DEBUG_MODE = false

Title Case and Sentence case

These are writing conventions rather than programming ones. Title Case capitalises the first letter of every word and is used for headings, article titles, and product names. Sentence case capitalises only the first word and is the standard for body text, captions, and UI labels in modern design systems.

Most major tech companies (Google, Apple, Microsoft) have shifted their UIs toward sentence case for labels and buttons — it feels more natural and conversational than title case.