A Sentence Case Converter converts data from one format to another using a deterministic mapping. It parses the input, transforms it according to the relevant standard, and returns a ready-to-use result. Only the first letter of each sentence (and proper nouns) is capitalized.
Sentence, title, upper, lower, camel, snake, kebab, and constant case.
Convert any text - including ALL CAPS, mixed case, or messy data - into proper sentence case where only the first letter of each sentence is capitalized.
The sentence case converter takes any text (ALL CAPS, mixed case, messy paste from a PDF) and returns it as lowercase prose with the first letter of each sentence capitalized. It is the everyday body-text style of English writing, distinct from title case and ALL CAPS.
Sentence case matters because it is the most readable default. Studies of reading fluency consistently find that all-caps text slows readers by roughly 10 to 15 percent: every glyph becomes a uniform rectangle, so the word-shape cues that fluent readers rely on disappear. Sentence case preserves ascenders and descenders, keeps the visual rhythm of normal prose, and signals where one thought ends and the next begins. That is why product UIs, news sites, and most modern style guides have shifted headings and buttons from Title Case toward sentence case over the last decade.
The tool above is broader than its name: it shows nine related transformations at once (sentence, title, upper, lower, camel, Pascal, snake, kebab, and constant case) so you can compare the same string across every convention a writer or developer needs. Everything runs in your browser; the text you paste never leaves the page.
The algorithm is a two-step regex transform: lowercase the whole string, then uppercase the first letter after the start-of-string, after sentence-terminating punctuation (period, exclamation mark, question mark) followed by whitespace, and after a newline.
step 1: s.toLowerCase() step 2: s.replace(/(^\s*\S|[.!?]\s+\S|\n\s*\S)/g, m => m.toUpperCase()) boundaries detected: - first non-space character of string - non-space character after . ! ? - non-space character after newline
Input: "THIS IS AN EXAMPLE. it's all caps AND lowercase MIXED. each sentence WILL BE FIXED."
| Style | Rule | Example | Use case |
|---|---|---|---|
| Sentence case | First letter of sentence + proper nouns | The quick brown fox. | Body prose, modern headings |
| Title Case (AP) | First letter of every major word | The Quick Brown Fox | Headlines, book titles |
| UPPER CASE | Every letter capitalized | THE QUICK BROWN FOX | Emphasis, legal warnings |
| lower case | No capitals | the quick brown fox | Casual, branded (e.g. bell hooks) |
| camelCase | First word lower, rest capped, no spaces | theQuickBrownFox | JavaScript / Java identifiers |
| PascalCase | Every word capped, no spaces | TheQuickBrownFox | Class names, types |
| snake_case | Lowercase, underscore separators | the_quick_brown_fox | Python / Ruby identifiers |
| kebab-case | Lowercase, hyphen separators | the-quick-brown-fox | URLs, CSS class names |
| CONSTANT_CASE | Uppercase, underscore separators | THE_QUICK_BROWN_FOX | Environment vars, constants |
toLowerCase(). Use locale-aware tooling for non-English copy.Sentence case capitalizes only the first letter of each sentence and any proper nouns. Everything else stays lowercase. It is the default style for body prose in English, contrasting with Title Case (every major word) and ALL CAPS (every letter).
It lowercases the input, then uppercases the first non-space character after the start of the string, after any period, exclamation mark, question mark followed by whitespace, and after a newline. Edge cases like abbreviations (Dr., U.S.A.) and ellipses are not corrected.
No. A pure algorithmic sentence case converter lowercases everything except sentence starts. Names like 'London', 'Apple', and 'I' get lowercased and must be re-capitalized manually. Heuristic detection of proper nouns requires NLP and produces false positives on common nouns.
Sentence case: 'The quick brown fox jumps over the lazy dog.' Title case (AP style): 'The Quick Brown Fox Jumps Over the Lazy Dog.' Sentence case is for body prose; title case is for headings, headlines, and book titles. Most blog and article copy uses sentence case for headings now.
No. The conversion runs entirely in JavaScript inside your browser tab. Nothing you type or paste is uploaded, logged, or stored, so it is safe for sensitive drafts, contracts, or unpublished copy. Closing the tab discards the text completely.