About whathappen.today
A small, fast site that answers “what day is it?” properly — for people, and for the programs and AI assistants that keep getting it wrong.
What you will find here
- Today's date in your own time zone, with ISO and US week numbers, the day of the year and the moon.
- Public holidays in 20 countries, each checked in that country's time zone, with substitute days, moon-sighting estimates and China's make-up working days.
- On this day in history for all 366 dates.
- Sunrise, sunset and twilight for more than 300 cities, moon phases, and a world clock.
- A free JSON API and MCP server with the same answers.
How it is built
Pages are plain HTML generated in advance and served from Cloudflare's network. The date, the time-zone conversions, sunrise and sunset, and the moon phase are calculated in your browser with JavaScript from your device clock, so the page needs nothing from us after it loads. The API runs the same code on Cloudflare Workers.
The astronomy follows published, public-domain methods: NOAA's solar equations and Jean Meeus's lunar formulas. We test them against the U.S. Naval Observatory: sunrise and sunset agree within two minutes at the places we checked, the moments of the moon's phases within twenty minutes.
Where the data comes from
- Public holidays: the open-source
holidayslibrary (MIT licence), compared for 2026 with government calendars from the UK, Japan, China, India and the Philippines. Each country page links to its official source. - History: English Wikipedia's date articles via the Wikimedia “On this day” feed (CC BY-SA 4.0), ranked with Wikidata (CC0).
- Cities: names and coordinates from Wikidata (CC0); time zones from the IANA time-zone database (public domain).
The full list of software and data licences is in licenses.txt.
What we do not do
There are no ads, no accounts, no cookies and no paid plans. We count page views with Cloudflare Web Analytics, which does not use cookies or identify visitors. Details are on the privacy page.
Corrections
Holiday rules change and data can be wrong. If you spot a mistake, email hello@whathappen.today — a link to the official announcement helps us fix it quickly.