How the count works
A word is a run of letters, combining marks or digits in any script. An apostrophe or hyphen between two letters keeps the word whole, so don't and well-known count as one word each.
Share = count ÷ total words × 100. With case ignored, The and the are the same word; with case-sensitive matching they are counted separately. Numbers can be excluded so that years and quantities do not crowd the list.
Worked example
"The cat sat on the mat. The dog sat on the cat." has 12 words and 6 distinct words. the appears 4 times, a 4 ÷ 12 × 100 = 33.33% share; cat, sat and on appear twice (16.67% each); mat and dog once.
Limits
Languages written without spaces between words, such as Chinese, Japanese and Thai, need dictionary-based segmentation, which this tool does not do; a run of such characters counts as one word. Stop words such as the and of are not removed, so they usually top the list.