File Name Case Converter
kebab-case writes hello-world-example. Lowercase filenames separated by hyphens survive every filesystem and every URL. The reason is case sensitivity: macOS and Windows treat Report.pdf and report.pdf as the same file, Linux does not — so a repository that works locally can break in CI purely on capitalisation. Hyphens also avoid the %20 encoding that spaces force in URLs.
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 |
Filenames Cross Case-Sensitive Boundaries
macOS and Windows treat Report.pdf and report.pdf as one file; Linux treats them as two. A repository that builds locally and fails in CI on a missing import is almost always this, and the error names a file you can see in the directory listing.
Lowercase also avoids the shell hazards: a leading hyphen parses as an option flag, spaces need quoting everywhere, and characters such as : and ? are illegal on some filesystems and merely awkward on others.
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
``