How sentences are detected
A sentence ends at a full stop, question mark or exclamation mark followed by a space or a new line. Common abbreviations (Mr., Dr., e.g., etc., a.m.) and decimals (3.5) don’t end a sentence. A line with no end punctuation, such as a heading or list item, counts as its own sentence.
What is a good sentence length?
Research summarised by the American Press Institute found readers understand more than 90% of sentences of 14 words or fewer, falling to under 10% at 43 words. An average of 15–20 words, with a mix of short and long, reads naturally.