Sentence Case Converter
Sentence case writes Hello world example. It capitalises only the first word, which is the house style for UI labels, button text and headings in most modern design systems — including Google Material and GOV.UK.
Conversions
| Input | Sentence 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 — and that is usually wrong, because proper nouns and genuine acronyms should keep their capitals. No algorithm can identify them without a dictionary.The Same Text in Other Cases
| Case | Result |
|---|---|
| camelCase | helloWorldExample |
| PascalCase | HelloWorldExample |
| snake_case | hello_world_example |
| SCREAMING_SNAKE_CASE | HELLO_WORLD_EXAMPLE |
| kebab-case | hello-world-example |
| Train-Case | Hello-World-Example |
Where Sentence case Fits
Sentence case is the house style of most modern interfaces and of many publications, including for headings and buttons, because it reads faster than Title Case and sidesteps the question of which words to capitalise. It is also the standard for form labels and error messages.
Converting in Code
``javascript
const sentence = (s) => {
const w = words(s).map((x) => x.toLowerCase());
if (w.length === 0) return '';
w[0] = w[0][0].toUpperCase() + w[0].slice(1);
return w.join(' ');
};
`
Applying sentence case to text containing names, brands or acronyms damages them irreversibly — NASA becomes Nasa and iPhone becomes Iphone. It is safe on machine-generated strings and unsafe on prose you did not write.
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
``