Sentence Case Converter (capitalize the first word of each sentence)

Understanding the sentence case converter — concept and principle

Sentence case writes text the way ordinary prose is written: a capital letter at the start of each sentence and small letters elsewhere. This converter fixes text typed with Caps Lock on, or normalises headings to sentence case, capitalises the word "I" and lets you keep existing capitals for names and acronyms.

How it is calculated

A new sentence starts at the beginning of the text, at each new line, and after ".", "?" or "!" followed by a space.

• The first letter of each sentence becomes a capital.
• Option 1: all other letters become small letters (fixes CAPS LOCK text).
• Option 2: other letters stay as typed (keeps names and acronyms).
• The word "I" on its own (also in I'm, I'll) is capitalised.

Counts: sentences started, characters changed, words.

The principle

Sentence case is the convention of ordinary writing and of many style guides for headings, including APA Style for some elements. A program can recognise sentence boundaries from punctuation, but it cannot know which words are proper nouns. That is why the safer option for already-correct text is to keep existing capitals, while the lowercase option is best for text typed entirely in capitals, followed by fixing names by hand.

Worked example

Default inputs: "THIS TEXT WAS TYPED WITH CAPS LOCK ON. can i fix it? yes! paste it here and it reads normally again.", lowercase other letters.

1. Sentences start at "THIS", "can", "yes" and "paste": 4 sentences.
2. All other letters are lowered, and the lone "i" becomes "I".
3. Result: This text was typed with caps lock on. Can I fix it? Yes! Paste it here and it reads normally again.
4. Characters changed = 33.
5. Words = 21.

How to read the result

Check the converted text for names, places, brands and acronyms, which a program cannot detect when lowering text. Abbreviations like "e.g." followed by a space are treated as sentence ends, so the next word may be capitalised unnecessarily. For titles that use title case, use a title case converter instead.

Common mistakes

• Lowercasing text that already had correct capitals for names.
• Expecting the converter to know proper nouns.
• Forgetting that abbreviations with full stops can split sentences.

Frequently asked questions

What is sentence case?

Capitalising only the first word of each sentence and proper nouns.

How do I fix text typed in all caps?

Use the lowercase option, then capitalise names by hand.

Does it capitalise "I"?

Yes, the standalone pronoun and contractions like I'm and I'll.

Is sentence case used for headings?

Many style guides use it for headings and interface text because it is easy to read.

Sources: APA Style, "Sentence case" (American Psychological Association) · The Unicode Standard 15.1, §3.13 Default Case Algorithms