Text Case Converter

Nine cases, and the three rules that decide the result

Three different jobs hide behind one button. A headline pasted out of a PDF arrives in capitals. A product name has a capital in the middle that has to survive. A column heading has to lose its spaces and become a variable. The nine cards above run all three on the same text at once, so you pick the one that came out right instead of guessing first.

Three rules decide what they do, and they are worth knowing before you trust the output:

• A word with a capital inside it is left alone in Title Case and Sentence case, so iPhone, eBay, JavaScript and McDonald keep their shape.
• A word in all capitals with two or more letters counts as an acronym and is also left alone, but only while the rest of your text has at least one lowercase letter in it.
• If every letter you paste is a capital, nothing is preserved. In a block of caps there is no way to tell an acronym from a shouted word, so the whole thing is rebuilt. That is what makes an ALL CAPS paragraph fixable at all.

The counters read what you typed, not the result, and count characters as code points: an accented letter is one, an emoji with a skin tone modifier is two. For sentences, paragraphs and bytes, use the word counter.

Which of the nine you actually want

• UPPERCASE: short labels and buttons. Whole paragraphs in caps are slower to read, and some screen readers spell them out.
• lowercase: the safe first step for anything that arrived shouting.
• Title Case: headlines, article titles, menu labels, slide headers.
• Sentence case: body text, form hints, alt text, anything that reads as prose.
• camelCase: JavaScript and Java variables, function names, JSON keys.
• PascalCase: classes, React components, Go and C# exported names, type names.
• snake_case: Python variables, database columns, and file names that survive a shell without quoting.
• kebab-case: URL slugs, CSS class names, npm package names.
• aLtErNaTiNg: the mocking meme format, and nothing else.

The four code cases run line by line, so a pasted column of headings comes back as a column rather than one run on name. Apostrophes are deleted instead of splitting a word, so don’t stop me now gives dontStopMeNow, not donTStopMeNow.

How to rescue a block typed with caps lock on

1. Paste the whole block in without fixing anything first. The acronym rule only stands down while the text is entirely capitals, and one lowercase letter switches it back on.
2. Read the Sentence case card for prose, or the Title Case card for a heading.
3. Repair the proper nouns and the acronyms. Nothing on the page knows that london is a city or that pdf was an abbreviation, and capitals destroyed the evidence before you got here.
4. Press Copy, paste it back over the original, and fix that handful of words. Still faster than retyping the paragraph.

How to turn a label into a variable, column or URL slug

1. Paste the labels one per line. A whole spreadsheet header row, pasted as a column, is converted line by line.
2. Pick the target: camelCase for JavaScript keys, PascalCase for a class or component, snake_case for Python and database columns, kebab-case for a URL or a CSS class.
3. Check the acronyms. XMLHttpRequest splits into xml_http_request and getUserByID into get-user-by-id, which is what most style guides ask for.
4. Decide what to do about accented letters, which are kept rather than stripped. For a URL, percent-encode the slug with the URL encoder or replace those letters by hand.
5. Check that nothing starts with a digit. This page formats, it does not validate, so 2nd_item comes out as typed and your compiler will object.

What Title Case leaves lowercase

Style guides disagree here: Chicago lowercases every preposition whatever its length, AP capitalizes those of four letters or more. The list used here is the practical middle, and short enough to check.

a, an, and, as, at, but, by, for, from, if, in, into, like, near, nor, of, off, on, onto, or, over, per, so, the, to, up, upon, via, vs, with, yet

The exceptions

• The first and last word of every lineis always capitalized, so A Room of One’s Own keeps its capital A.
• So is a word straight after a colon, full stop, question mark or exclamation mark, which is what makes Star Wars: The Empire Strikes Back come out right.
• Hyphenated compounds are judged part by part: state-of-the-art becomes State-of-the-Art, not State-Of-The-Art.
• The checkbox above the cards ignores the list completely. That style is usually called start case, and it is what the PROPER function does in Excel and Google Sheets.

Sentence case uses none of this. It capitalizes the first word of each sentence, keeps the preserved words described above, and restores the pronoun I along with I’m, I’ll, I’ve and I’d, the only single letters English capitalizes mid sentence by rule.

Getting the result out of the page

• Copy button: each card copies its own result. Paste with Ctrl+V, Cmd+V on a Mac, or a long press on a phone.
• If the copy fails: the in-app browsers inside Instagram, Facebook and LINE sometimes refuse clipboard access, and a warning says so. Select the text in the card and copy it by hand, or open the page in Safari or Chrome.
• Paste as plain text with Ctrl+Shift+V, or Cmd+Shift+V on a Mac, when the destination would inherit formatting.
• Line breaks survive every mode, so a list pasted in comes back as a list and drops straight into a spreadsheet column.
• Nothing is in the address bar. Your text is never written into the URL, so a copied link shares the tool, not what you typed.

The same job in an editor, a spreadsheet and CSS

• Word: select the text and press Shift+F3 to cycle lowercase, capitalized and uppercase, or use the Aa button on the Home tab.
• Google Docs: Format, then Text, then Capitalization.
• Excel and Google Sheets: =UPPER(), =LOWER() and =PROPER(). PROPER is start case, so it capitalizes the a and the of too.
• VS Code: the command palette has Transform to Uppercase, Lowercase, Title Case and Snake Case, none of them bound to a key by default.
• CSS: text-transform changes how text is drawn, not what the text is. Copy it out, read it with a screen reader or index it with a crawler and you get the original back.
• Terminals: tr a-z A-Z only handles unaccented ASCII. Prefer awk with toupper and tolower, and expect none of them to know the rule below.

Where language changes the answer

Case belongs to the writing system, not to the alphabet. In Turkish and Azerbaijani the dotted and dotless i are separate letters, so the capital of i keeps its dot and the lowercase of I loses it. This page follows your browser language setting, so a Turkish browser gets the Turkish answer: correct there, surprising anywhere else. Greek differs again, lowering a word ending in sigma to the final form of the letter. Both come from the Unicode case mapping data, not from anything invented here.

What it cannot know

• Proper nouns cannot be recovered. Sentence case will not capitalize london or anna for you. Read the result before you ship it.
• Abbreviations end sentences early. A new sentence starts after any full stop, so the word after e.g. or Dr. gets a capital it should not have. Decimal numbers are safe, because a digit is not a letter.
• Case changes are not always reversible. The German sharp s becomes two letters when uppercased and never comes back; ligatures behave the same way. Check the length before pasting into a field with a limit.
• Some scripts have no case. Chinese, Japanese, Korean, Arabic, Hebrew and Thai pass through every mode unchanged. That is the right answer, not a failure.
• aLtErNaTiNg breaks accessibility. Screen readers often spell it out, and search engines treat it as a different string from the normal spelling. Keep it to jokes.
• Never run a password or key through it. Changing the case of a secret changes the secret, and there is no undo once you have pasted the result over the original.