CSS Class Name Converter
kebab-case writes hello-world-example. CSS class names are conventionally kebab-case — nav-item, card-header, is-active — because CSS is case-insensitive for keywords and hyphens read as word breaks in selectors. HTML attribute names and custom data attributes follow the same rule, and data-user-id maps automatically to dataset.userId in JavaScript.
Conversions
| Input | kebab-case |
|---|---|
hello world example | hello-world-example |
XMLHttpRequest | xml-http-request |
user_first_name | user-first-name |
Total Order Count | total-order-count |
XMLHttpRequest becomes xml-http-request. That is the correct behaviour for a URL or a CSS class, where case sensitivity varies by context and mixed case causes more problems than it solves.The Same Text in Other Cases
| Case | Result |
|---|---|
| camelCase | helloWorldExample |
| PascalCase | HelloWorldExample |
| snake_case | hello_world_example |
| SCREAMING_SNAKE_CASE | HELLO_WORLD_EXAMPLE |
| Train-Case | Hello-World-Example |
| dot.case | hello.world.example |
Naming Classes People Can Read
A class name is read far more often than it is written, and the useful ones describe what an element *is* rather than what it looks like. promo-banner survives a redesign; red-box-large becomes a lie the moment the brand colour changes.
CSS is case-insensitive for keywords, but the browser matches class names in the HTML case-sensitively, so navItem and navitem are different classes. Lowercasing removes the whole category of bug where a selector silently matches nothing.
Converting in Code
``javascript
const kebab = (s) => words(s).map((w) => w.toLowerCase()).join('-');
`
A hyphen is a subtraction operator in most languages, so kebab-case identifiers cannot be used unquoted in code. That is precisely why it belongs in URLs, CSS and filenames and not in variable names.
Converting at the API Boundary
The recurring friction is that JavaScript uses camelCase and Python, Ruby, Go and SQL use
snake_case. The fix is to convert in exactly one place — the client that talks to the API —
rather than letting both conventions into the same codebase.
`javascript
const toCamel = (s) => s.replace(/_([a-z])/g, (_, c) => c.toUpperCase());
const toSnake = (s) => s.replace(/[A-Z]/g, (c) => '_' + c.toLowerCase());
// Recursively, for a whole payload
const convertKeys = (value, fn) =>
Array.isArray(value)
? value.map((v) => convertKeys(v, fn))
: value && typeof value === 'object'
? Object.fromEntries(Object.entries(value).map(([k, v]) => [fn(k), convertKeys(v, fn)]))
: value;
`
Two things to watch: keys that are user data rather than field names must not be
converted, and the round trip is not always lossless — userID → user_id → userId
changes the original.
Where Each Convention Is Mandatory
Not stylistic — these will break if you deviate:
| Context | Requirement |
|---|---|
| Environment variables | Uppercase with underscores; POSIX reserves lowercase |
| Custom HTML elements | Must contain a hyphen |
| Python modules | Cannot contain hyphens; the import statement will not parse |
| SQL identifiers | Folded to one case unless quoted, so camelCase does not survive |
| React components | Must start uppercase, or JSX treats it as an HTML tag |
Renaming Safely
A find-and-replace across a codebase will hit strings, comments and unrelated identifiers.
Use your language server's rename symbol instead — it understands scope. For a bulk rename
across files, restrict the pattern with word boundaries and review the diff before
committing:
`bash
grep -rn '\buserId\b' src/ # look first
``