Original
Rewrapped
How it decides
Breaks it removes
In Auto mode the tool measures how wide the text was wrapped — roughly the longest line it can find — and treats any line that comes close to that width as a line the wrapper cut off mid-thought. Those breaks are removed and the lines are joined with a single space.
Breaks it keeps
A line that stops well short of the wrap width was almost certainly the end of a paragraph, so its break is kept. Blank lines are always kept, and so are breaks in front of headings, list items, table rows, indented code and a change of > quote depth.
When auto guesses wrong
Switch to Manual and set the cutoff yourself — lower it if paragraphs are being run together, raise it if one paragraph is being split in two. Blank lines only is the blunt instrument: join everything that isn’t separated by an empty line.
Nothing is uploaded
All of this runs in your browser. The text never leaves your machine, there is no server to send it to, and closing the tab is all the cleanup there is.