About Koyomi
Koyomi turns a CSV or Excel spreadsheet of events into a standard .ics calendar file that Google Calendar, Outlook and Apple Calendar can import. It is free, it needs no account, and your spreadsheet never leaves your device.
Why it exists
Schedules usually start life in a spreadsheet: a class timetable, a shift rota, a season of fixtures, a conference programme. Getting those rows into a calendar is harder than it should be. Each calendar app expects its own column names and date format, a single wrong time zone shifts every event, and the usual advice is to retype everything by hand.
Koyomi was built to make that a one-minute job. You drop the spreadsheet, check that the columns were matched correctly, and download one file that every major calendar accepts.
How it works
The file is read in your browser, with PapaParse for CSV and SheetJS for Excel workbooks. Koyomi looks at the header row and the cell values to work out which columns hold the title, the start and end, the location and the notes, and it accepts the common date and time formats instead of demanding one. You can correct any column it guessed wrong before exporting.
The output is a plain iCalendar file with the time zone written into it, so events land at the right hour wherever they are imported. There is no server step. Koyomi has nowhere to send your spreadsheet, which matters when the rows contain names, addresses or client details.
What it does not do
Koyomi produces a file for you to import. It does not connect to your calendar account, does not ask for calendar permissions, and cannot edit events after you import them.
Who makes it
Koyomi is made by Nathan Stewart at I4C Studio, a one-person product studio that builds developer tools and small, single-purpose web tools. The same person writes the code, the guides on this site and the replies to your email.
The studio's other free browser tools work the same way, on your device with no upload:
How it is paid for
Koyomi is free to use, with no account, no trial and no paid tier. Advertising through Google AdSense covers the hosting. The ads are the only part of the site that involves a third party beyond hosting and aggregate analytics, and the privacy page explains exactly what that means.
Where to start
Found a file that will not convert, or a mistake in a guide? The contact page says how to report it.