09 · Side project 2026 · Rairai ristikot

A Crossword App in Three Days

My friends and I wanted to make crosswords for each other. How hard could it be to build an app for that?

MethodThree documents before any code: rules for the AI pair, a roadmap where every decision carries a date and a reason, and one spec per feature with a phone walkthrough. The look was settled in 13 sketch rounds, one question at a time.

What was builtA Finnish-style crossword app for a closed group of friends: a pile of sheets on a desk, a solver on the phone's own keyboard, a boundless creator with drawn clues, magic-link login, live on Cloudflare Pages. 68 dated decisions, 91 engine tests, three days.

What I learnedThe method is the product. With rules, roadmap and specs in place, the AI writes the code and I make the calls: what the home screen is, what the stamp does. Friends' phone tests became the next dated decisions.

(Re)design

A sketch page titled What object is the home screen, with three drawn options side by side: a pile of cream puzzle sheets on a desk, a filing drawer with tabbed folders, and a desk with a pile and a drawer beneath it, each with a short note on what it gets right and wrong — Two sketch rounds. Above, from the design session on 14 September 2026: three drawn answers to what the home screen is. The pile won; the drawer waits on the backlog. Below, the comments feature a day later: the sheet turns over to its comments, and the sliders set how the paper bows, where it hinges and where the arrow lands.

The app on a phone: the Rairai ristikot heading in heavy black type, a pile of cream puzzle sheets slightly askew with an orange crossword grid on the top one, and a pad of grid paper beneath labelled Uusi ristikko — The app on a phone: the pile on the desk, a puzzle being built in the creator, and a sheet turned over to the comments on its back.

The creator on a phone: a sheet in wine red ink titled Saunailta on faint grid paper, with the words SAUNA, UIMARI, SÄÄ and ALLAS crossing, four ink clue cells, the cursor on the next empty square, and the ink, language, clue and publish controls above — The app on a phone: the pile on the desk, a puzzle being built in the creator, and a sheet turned over to the comments on its back.

The storyA kitchen-table idea: friends who make crosswords for each other and wanted them on a phone. The first evening set up the working method, the second day was the design session, and the app was live on the third, with a privacy notice, a fake backend for login-free previews and a browser rig that clicks through every screen on desktop Chromium, Android and iPhone. A few friends have tested it on their phones. Try the desk below: a preview build with example puzzles and no login.

The Rairai ristikot desk in a browser: the heading top left, a pile of cream sheets in the middle with an orange crossword on top, and a pad of grid paper below it — Rairai ristikot, live in the page. Flick through the pile, lift a sheet and type, or tap the pad to make a puzzle. A preview build with example puzzles, so nothing you do here reaches anyone.

A Crossword App in Three Days

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Questions or thoughts? I'd love to hear from you!