How the conversion works
The whole text is lowercased first. Then the very first letter is capitalized, along with any letter that follows a period, question mark, or exclamation mark plus at least one space or line break. That is the entire rule, and knowing it is the difference between using the tool well and being surprised by it.
The letter matching is Unicode-aware, so an accented first letter or a first letter in a non-Latin alphabet is capitalized correctly rather than skipped.
There are no options and no toggles. The result updates on every keystroke and a Copy result button appears once there is output.
- Paste the text on the left
- The sentence-cased version appears immediately
- Press Copy result
The lowercase pass is destructive
Because the entire text is lowercased before anything is capitalized, capital letters that were correct do not survive. Proper nouns lose their capital: London becomes london, Sarah becomes sarah. Acronyms are flattened: NASA becomes nasa, HTML becomes html. The standalone pronoun I becomes i. Brand names with internal capitals lose them too.
There is no exception dictionary, no name list, and no option to preserve existing capitals. That is a real limitation, and the honest way to use this tool is to treat it as step one: convert the case, then read through and fix the proper nouns by hand.
The trade is worth it for the case it was built for. A heading or a paragraph in ALL CAPS has no capitalization information left to preserve anyway, so lowercasing everything costs nothing and the tool restores exactly what can be restored.
Where the sentence detection misses
The rule needs whitespace after the terminal punctuation. If a period is followed immediately by the next letter, as in "done.Next", nothing is capitalized. Text scraped from a web page or copied out of a PDF often has that exact shape.
A closing quote or bracket between the period and the next word also blocks it. In the sequence "he said." followed by a new sentence, the character right after the period is a quote mark, not a letter, so the rule does not fire.
Abbreviations cause the opposite error. There is no exception list, so "e.g. this" and "Mr. Smith" get a capital after each internal period, because as far as the rule is concerned those are sentence ends. A new line that is not preceded by terminal punctuation is not capitalized either, which affects bulleted lists.
- Needs a space or line break after the period to fire
- A quote or bracket after the period blocks it
- Abbreviations like e.g. and Mr. produce false capitals
- List items without terminal punctuation stay lower case