よんじゅうびょう。
Free · play online in your browser, no download
Forty seconds until the light turns green: jump the bicycles and joggers, let the pigeons pass. A one-button action game for the browser, its code written almost entirely by Claude Code.
Official site vannangames.com, verified Nov 3, 2026. Play address linked from the game's page on VANNAN GAMES (vannangames.com), the developer's own site, which the developer's Zenn article links.
Where to play
Every platform this game is on. Links are checked against official sources; we never host or mirror games.
- Play free — official siteBrowserReleasedFree
Runs in a desktop or mobile browser. No download.
Browser (no download) · Mobile · Official link verified Nov 3, 2026.
About よんじゅうびょう。
よんじゅうびょう。 is a free one-button action game for the browser, in Japanese, set at the crossing from the developer's novel 四十秒の交差点, where the light is mean about when it changes. Instead of waiting out the forty seconds, you run through them. The only action is jumping, by tap, click or the space bar, and holding longer jumps higher. Bicycles are the fastest and need an early jump; joggers are slower but tall enough to catch a low jump; flocks of pigeons cross the sky, so jumping takes you into them and the right move is to run on; puddles do not trip you but make your footing slip before the next obstacle. Survive forty seconds and the light turns green, you cross, and the “second today” begins, with faster and denser obstacles each loop; the record is how many “todays” you reach. Dodging an obstacle at the last moment gives a near-miss bonus, which the developer added so that jumping early and high would not be the safe answer every time. Rarely, once per play, someone catches you by the sleeve as you are about to fall, a line the developer says may give players of the novel pause. A play lasts from forty seconds to a few minutes, and the best score is saved in the browser. It was one of the two games the VANNAN GAMES site opened with. Per the developer, kawaiy, the code is almost all written by Claude Code; the illustrations were generated with ChatGPT. Plain HTML, CSS and JavaScript with no framework. Free in desktop and phone browsers.
How it was built
VerifiedIn a Zenn article (23 Aug 2026) about building the eight-game VANNAN GAMES site in 34 days, the developer lists the division of work as “Claude : コード、ドキュメント、シナリオの下書き、レビュー” (Claude: code, documents, scenario drafts, reviews) and writes “コードはほぼClaude Codeに書かせています。” (I have Claude Code write almost all of the code.) Check and generator scripts run from a Claude Code Stop hook after every agent reply and again on GitHub Actions.
- DeveloperA production note on the site (17 Sep 2026) opens: “このサイトは、コードを書く作業の大半をAIに頼んで作っています。” (This site is built by leaving most of the code writing to AI.) — VANNAN GAMES
Generated the illustrations; the game's page credits “イラスト：ChatGPTで生成” (illustrations generated with ChatGPT).
Plain HTML, CSS and JavaScript with no framework, served as static files from Tencent Cloud EdgeOne Pages; the best score is saved in the browser's localStorage. Claude Code writes almost all of the code under checks run by a Stop hook; ChatGPT generates the illustrations. The game has sound effects; its page credits no music.
- Engine / framework
- None (vanilla JavaScript)
- Languages
- JavaScript
- Team size
- 1 (solo)Developer ReportedVANNAN GAMES
- Development time
- Not disclosed
- Development cost
- Not disclosed
- AI-written code
- Not disclosed
“コードはほぼClaude Codeに書かせています。”- Eight browser games in 34 days: Claude, ChatGPT and Suno, and what could not be handed off (Zenn, Japanese)
- Game page on VANNAN GAMES (Japanese)
Verification notes: AI use and the workflow come from the developer's Zenn article (23 Aug 2026, 02:03 JST), re-read through Zenn's API on 8 Nov 2026; it links vannangames.com. The article covers the whole site (eight games on 23 Aug 2026) and does not name this game, so the Claude Code statement is applied to each of its games. A production note on the site (17 Sep 2026) also says most of the code writing is left to AI. Rules, obstacles, design notes and credits (企画・開発：kawaiy; illustrations generated with ChatGPT; no music credit, sound effects only) come from the game's page, read on 8 Nov 2026. Release date: the updates log says the site opened on 20 Jul 2026 with 四十秒の交差点 and this game; the game's page shows 公開日 30 Jul 2026, when the log says its introduction page was added, and last updated 2 Aug 2026. Note the addresses: this game plays at /games/yonjubyo40/, while /games/yonjubyo/ is the separate novel 四十秒の交差点, already listed. The site's operator page names kawaiy (個人) as the operator. The English title is our translation; there is no official English title. The game's script contains no AI service addresses; the site loads Google Analytics. The Japanese interface was observed (lang="ja"); no other language option was found. The game was not played.
Development history
Released on VANNAN GAMES; the site opens with this game and 四十秒の交差点.
DeveloperVANNAN GAMESThe developer's Zenn article describes building the eight-game site with Claude Code writing almost all of the code.
DeveloperZenn (kawaiy)
Game performance
Each figure measures something different — concurrent players, owners, downloads and sales are never interchangeable and are never added together. Labels show where each number comes from.
Browser (official site)
Free in modern desktop and phone browsers, with no install or account; the best score is saved in the browser and not sent anywhere, per the game's page. The site accepts optional support through OFUSE.
No public metrics recorded for this listing.
Not publicly available: Concurrent players (site), Monthly revenue, Gross revenue.
Sales & revenue (all platforms)
Browser game — there are no downloads to count.
Reviews & rankings
Not yet reviewed by our editors.
Not currently ranked.
Sources
| Source | Type | Published | Accessed |
|---|---|---|---|
| 34日でブラウザゲーム8本のサイトを立てた。Claude・ChatGPT・Sunoの分担と、丸投げできなかったもの Zenn (kawaiy) · Japanese | Devlog | Aug 23, 2026 | Nov 3, 2026 |
| よんじゅうびょう。｜40秒を生き延びるワンボタンアクション｜VANNAN GAMES VANNAN GAMES · Japanese | Official site | Jul 30, 2026 | Nov 3, 2026 |
| 更新情報｜VANNAN GAMES VANNAN GAMES · Japanese | Official site | Not confirmed | Nov 3, 2026 |
| ルールを決めた8日後に、自分でそれを破った——AIへの指示を4つのレイヤーに分けた｜VANNAN GAMES 制作ノート VANNAN GAMES · Japanese | Devlog | Sep 17, 2026 | Nov 3, 2026 |
| VANNAN GAMESについて｜運営者情報 VANNAN GAMES · Japanese | Official site | Not confirmed | Nov 3, 2026 |
| Official game page (language check) VANNAN GAMES | Official site | Not confirmed | Nov 3, 2026 |
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