Case Converter: Stop Retyping the Same Sentence
You pasted a heading from a CMS and it's ALL CAPS. Or you're writing a constant name and need SCREAMING_SNAKE_CASE from a sentence. Or a designer handed you title case copy and your component expects sentence case.
Retyping it is dumb. This tool converts text between seven case styles instantly — sentence case, lowercase, UPPERCASE, Capitalized Case, Title Case, aLtErNaTiNg CaSe, and iNVERSE cASE. Paste in, pick your style, copy out. Live character, word, sentence, and line counts included.
Runs in your browser. Nothing leaves your machine.
What's actually happening
Each transformation operates on your input character by character or word by word, depending on the style.
Sentence case capitalizes the first letter of each sentence and lowercases everything else. It looks for ., !, and ? as sentence boundaries.
Title Case follows AP style — it capitalizes most words but keeps short articles and prepositions lowercase (a, an, the, in, on, at, etc.). The first and last words are always capitalized regardless.
aLtErNaTiNg CaSe toggles upper/lower on every alphabetic character, skipping non-letters. So spaces and punctuation don't break the alternation pattern.
iNVERSE cASE swaps the case of every character — uppercase becomes lowercase and vice versa.
The rest are straightforward: toLowerCase(), toUpperCase(), and capitalizing the first letter of every word for Capitalized Case.
Using it
Paste or type your text. Click the case style you want. The output updates immediately. Hit Copy to grab it, or Download to save as a .txt file.
Ctrl+Enter applies Sentence case as the default. Ctrl+K clears everything.
Title Case is harder than you think
Most case converters just capitalize every word. That gives you "The Cat Sat On The Mat" — which looks wrong. Proper title case keeps small words lowercase: "The Cat Sat on the Mat."
This tool follows AP style conventions for stop words. It lowercases articles (a, an, the), conjunctions (and, but, or), and short prepositions (in, on, at, to, for, of, by). First and last words are always capitalized.
If you need a different title case convention (like Chicago Manual of Style), you'll need to tweak the output manually. But AP style covers 90% of use cases.
Edge cases
Mixed scripts — case conversion only affects Latin characters. Chinese, Japanese, Arabic, and other scripts pass through unchanged. This is correct behavior — those scripts don't have a concept of upper/lower case.
Accented characters — é correctly becomes É in uppercase. JavaScript's built-in toUpperCase() handles Unicode properly for Latin-extended characters.
Abbreviations in Title Case — "NASA launches new satellite" becomes "Nasa Launches New Satellite" because the tool doesn't know "NASA" is an acronym. There's no reliable way to detect this automatically. Fix these manually.
Sentence detection — sentence case relies on ., !, and ? as boundaries. If your text uses periods in abbreviations (like "Dr. Smith"), it'll capitalize the next word. Not perfect, but good enough for most text.
Troubleshooting
Title Case lowercased my acronym — the tool can't distinguish between regular words and acronyms. "API" becomes "Api" because it only capitalizes the first letter of each word. Manually fix acronyms after conversion.
Sentence case capitalized mid-sentence — your input probably has a period that's not a sentence boundary (like "U.S." or "e.g."). The tool sees the period and capitalizes the next character.
Alternating case looks wrong — the alternation is per-letter, not per-character. Spaces, numbers, and punctuation are skipped. So hello world becomes hElLo wOrLd, not hElLo WoRlD.
My text stats don't match my word processor — different tools count words differently. This tool splits on whitespace, so hyphenated words count as one word. Some word processors count them as two.
Downloaded file has wrong encoding — the download outputs UTF-8 text. If you open it in an editor that defaults to a different encoding, accented characters might look garbled. Set your editor to UTF-8.
Alternatives
For bulk processing in code, JavaScript's toUpperCase(), toLowerCase(), and a custom title case function cover everything this tool does. But for one-off conversions, this is faster than writing a throwaway script.