Case Converter

Convert text between uppercase, lowercase and other case formats

This converter offers five rewrites — Uppercase, Lowercase, Title case, Sentence case and Alternating case — applied live as you type on the left. It changes the case of letters and touches nothing else, so digits, punctuation, spacing and any non-cased script pass through exactly as they arrived. The rewriting runs in your own browser and the text is never transmitted.

How to use it

  1. Pick a mode from the row of buttons at the top: Uppercase, Lowercase, Title case, Sentence case or Alternating case. The active one is highlighted in the accent colour.
  2. Paste into the box labelled Input on the left. Conversion is live — edit the text or switch modes and the Output box updates immediately, with nothing to confirm.
  3. The Output box is read-only, so change the source text on the left instead. Copy, at the bottom right, takes the result away; Clear, on the left, empties the input box only.

When it comes in handy

Normalising SQL and configuration keywords

One colleague writes select, another writes SELECT, and the diff becomes noisy. Run the fragment through Uppercase and paste it back to settle the argument. Do check the result: the transformation is indiscriminate, so anything inside a string literal is shouted too.

Rescuing ALL-CAPS exports from legacy systems

Names and addresses out of an ERP, a bank statement or an open-data dump often arrive as CHEN MEI LING — fine for a mainframe, aggressive on an envelope. Flatten it with Lowercase, then lift each word with Title case, and two passes give you something readable. The same pair tidies a whole table of contents in one paste.

Producing the mocking alternating-caps meme style

tHiS kInD oF tExT reads as sarcasm on social platforms, and typing it by hand is tedious enough to kill the joke. Because the alternation follows character position rather than letter position, adjusting the spacing changes which letters end up capitalised.

Limits and behavior

  • Title case raises the first letter after each word boundary and leaves every other letter alone, so HELLO world becomes HELLO World — existing capitals are never lowered. For a proper title-style result, run Lowercase first.
  • Underscores count as word characters in the boundary rule, so hello_world becomes Hello_world and nothing more. Apostrophes and hyphens do not, which is why don't becomes Don'T and e-mail becomes E-Mail. Accented letters fall outside the rule too: école comes back as éCole, because é reads as a separator and the capital lands on the wrong letter.
  • Sentence case lowercases the entire passage first and then raises the letter after a full stop, question mark or exclamation mark, so every proper noun and acronym is a casualty of that first step — iPhone becomes iphone, API becomes api. The boundary it looks for is punctuation followed by whitespace, so over.next gets no capital while 3.5 kg wrongly becomes 3.5 Kg. A bare line break with no sentence-ending punctuation before it does not start a new sentence either.
  • Alternating case alternates by index: characters at positions 0, 2 and 4 are upper, the rest lower. Spaces, punctuation and line breaks each occupy a position, so the effect is every other character rather than every other letter.
  • Conversion uses the browser's built-in methods rather than an ASCII-only table, so ü becomes Ü. German ß expands to SS in uppercase, which lengthens the string and cannot be reversed, and the conversion is locale-independent, so Turkish dotless i is not handled by its local rule. Han characters, kana and Hangul have no case distinction and pass through untouched.
  • There is no camelCase or snake_case conversion here. None of the five modes adds or removes a character, and none inserts or deletes spaces or underscores. Your text is rewritten by code already loaded in this tab and goes nowhere else; the page itself, like the rest of the site, does load third-party resources such as advertising.

Frequently asked questions

Why did Sentence case turn iPhone into iphone?

Because the mode starts by lowercasing the whole passage and only then restores capitals after sentence-ending punctuation, at which point there is no way to know which words were brand names. It is a deliberate trade-off: without the flattening step, text pasted from an ALL-CAPS source could not be fixed at all. When iPhone and API have to survive, use Title case, which leaves existing capitals in place.

Why does Title case give me Don'T?

The apostrophe is not a word character, so a fresh word boundary forms in front of the t and the first-letter rule fires there. Hyphens behave the same way: state-of-the-art comes back as State-Of-The-Art. If such words are rare, fixing them by hand afterwards is quickest; for bulk work, run Lowercase here and let find-and-replace handle the capitals.

Can it produce camelCase or snake_case?

No. This tool only rewrites the case of letters — it never deletes a space or inserts an underscore, and deciding what happens to those separators is precisely what those naming conventions are about. For real identifiers, multiple cursors in an editor or a few lines of script fit better.

Is any of this recorded?

No. All five modes are a few lines of JavaScript in this tab; they run on your device and finish there, neither the input nor the output is transmitted, and a page reload clears both. To be explicit about what the page does do: it loads third-party resources such as advertising, and those connections carry information about the page rather than the text you are converting.