Release notes are the document that ships alongside a specific version or update, answering one question: what changed? New features, bug fixes, deprecations, known issues. One release, one set of notes.
They're often confused with a changelog, but they're not the same thing. A changelog is the running history of everything shipped over time. Release notes are a single entry in that history.
Developers integrating your API want to know if anything broke. Admins managing enterprise accounts need to know what changed before their users ask. Power users notice every UI shift. If you don't write release notes, these people get surprised in production.
Good release notes are short and specific. "Improved performance" tells nobody anything. "Dashboard load time reduced by 40% for accounts with over 1,000 items" is useful. Skip the marketing language. Just say what changed and what it means for the reader.
The format is simple: a short summary at the top, then a grouped list of new features, improvements, bug fixes, and deprecations. If a change requires user action, call it out explicitly at the top, not buried in the middle.
Writing release notes also forces your team to clearly articulate what shipped. If you can't write the note, you might not fully understand what you built.