Enter a version number and date, then list Added/Changed/Fixed bullet points, and the tool formats them into a Keep a Changelog-style CHANGELOG.md entry you can prepend to your file.
Yes. Entries follow the Keep a Changelog convention — versioned headings with Added, Changed, and Fixed sections — which most changelog readers expect.
Yes, as a starting point — review names, paths, and details against your actual project before committing.
No. Everything is built client-side in your browser; nothing is sent anywhere until you commit it yourself.