AI Bookkeeper already had a calendar command. Most people who need it will never open a terminal, so it is now a page: pick a tax year, a state and a filing frequency, tick payroll or contractors, and get the dates as a list or one .ics file with a reminder a week ahead. It runs in the browser and uploads nothing.
Testing it in a real browser found a bug the command line never showed: the file writer used Node's Buffer to fold long lines, so the download threw in every browser. It uses TextEncoder now, and a test removes Buffer to keep it that way.
What to trust. The federal dates and the sales tax presets are the ones the tool already used. Some state presets were read from the state's own page, the rest from search excerpts and third-party guides, and the page says to confirm yours. The 2027 IRS inflation figures are still not published, so nothing here depends on them.