Monthly · public countdown
Build-a-thon
One prompt a month, open from the 1st to the last day. This is a calendar, not a competition: no prizes, no scoring, no submission form that quietly becomes a mailing list. Build the thing, then post it wherever you already post.
Open now
One-screen hero
2026-09-01 → 2026-09-30 · September 2026
18days left
40% through the window. The countdown is computed from your own clock; the server rendered 2026-09-12 when this page was built, and the dates above are arithmetic on the month, not a list someone forgot to update.
Closes on 2026-09-30. There is no submission form and no leaderboard: build it, then link it wherever you normally post.
Opens on 2026-10-01. The theme rotates by month, so a challenge cannot be announced after it has already closed.
Opens on 2026-11-01. The theme rotates by month, so a challenge cannot be announced after it has already closed.
How the calendar works
The window is arithmetic on the month — open on the 1st, close on the last day — and the theme is themes[monthIndex % themes.length]. Nothing is hand-maintained, so there is no way for this page to advertise a challenge that finished last week, which is the usual failure mode of an events page.
Countdown honesty
The page is prerendered, so the server rendered its own build date (2026-09-12). The countdown you see is recomputed from your clock when the page runs, and the panel says which clock it used. A countdown that quietly borrowed the server's date would be wrong for anyone in a different timezone.
Related: the weekly community day runs every Thursday with a smaller brief, and the challenge archive keeps the older briefs with their outcomes.