MACH RUN
Free · play online in your browser, no download
Fly a jet low and fast down a valley that never ends, under bridges and onto moving carriers, and stay under the radar. The developer says Opus 5.5 built it from essentially one prompt.
Official site jebkj21.itch.io, verified Nov 3, 2026. Linked as “MACH RUN by JebKJ21” in both of the developer's own Reddit posts (r/vibecoding and r/aigamedev).
Where to play
Every platform this game is on. Links are checked against official sources; we never host or mirror games.
- Play free — itch.ioitch.ioReleasedFree
Plays in the browser on itch.io. No download.
Browser (no download) · Mobile · Official link verified Nov 3, 2026.
About MACH RUN
MACH RUN is a free endless flight game in the browser. You fly a jet down a procedurally generated valley that changes as you go, with day turning into night: the lower and faster you fly, the more you score. Near misses, rings, flying under bridges and rock arches, and touch-and-go landings on moving aircraft carriers build your multiplier, while radar sites and enemy jets lock on if you climb too high, so you carry missiles, a gun and flares. The run ends when you hit the terrain or get shot down. There is a world leaderboard where every score is saved with its valley, so you can fly the exact valley the top player flew, plus a daily valley that is the same for everyone, night vision, a tutorial, a cockpit view and an arcade control option. The developer, a self-described flight-sim fan, wanted semi-realistic flight physics in an unrealistic environment and strongly recommends a gamepad or joystick; it also plays with keyboard, mouse (press C) or on a phone or tablet with an on-screen stick or tilt. On Reddit the developer says Opus 5.5 built it from essentially one prompt over a weekend, getting the look, gameplay and mechanics right first time, and that the rest of the weekend went into extra features. Free on itch.io. In English.
How it was built
Partially verifiedOn r/vibecoding (27 Sep 2026, UTC) the developer writes: “One shot this old idea of mine in a weekend, Opus 5.5 got the aesthetics, gameplay and mechanics all first try, I just spent the rest of the weekend adding extra features.” The r/aigamedev post of 2 Oct 2026 is titled “MACH RUN - Built by opus 5.5 in essentially one prompt.” The posts name only the model, not the app or tool it was used through, and do not say how the later features were made.
- DeveloperPost title: “MACH RUN - Built by opus 5.5 in essentially one prompt.” — Reddit (u/Jeb_the_killer)
- Developeritch.io AI disclosure: AI Assisted, Code, Graphics. — itch.io
Built over a weekend from essentially one prompt to Opus 5.5, then extended with extra features, per the developer; regular updates followed on itch.io (sound overhaul, playtest fixes, flight-stick support, cockpit view, tutorial and free flight). The browser build is a bundled Three.js game (observed), and the leaderboard runs on a Cloudflare Worker.
- Engine / framework
- Three.js
- Languages
- JavaScript
- Team size
- Not disclosed
- Initial build time
- A weekend, from essentially one promptDeveloper ReportedReddit (u/Jeb_the_killer)
- Development time
- Not disclosed
- Development cost
- Not disclosed
- AI-written code
- Not disclosed
“One shot this old idea of mine in a weekend, Opus 5.5 got the aesthetics, gameplay and mechanics all first try, I just spent the rest of the weekend adding extra features.”Verification notes: AI use comes from the developer's posts by u/Jeb_the_killer on r/vibecoding (27 Sep 2026, 21:57 UTC) and r/aigamedev (2 Oct 2026, 16:49 UTC), read from the Arctic Shift Reddit archive on 5 Nov 2026; both link the itch.io page as “MACH RUN by JebKJ21”. The Reddit and itch.io names differ, so the tie rests on the posts' first-person wording and links. Opus 5.5 is quoted as written; the tool used with it is not named, and no AI code share is given. Gameplay, controls, the Released status, genres, the English language field, the AI disclosure and the itch.io rating of 5.0 (3 ratings) come from the itch.io page, re-read on 5 Nov 2026 (updated 10 Oct 2026, 19:58 UTC). The itch.io page does not show a publication date; the game was public by the first post, so no release date is recorded. The build's scripts (loaded 5 Nov 2026) call no AI services; their only outside services are Google Fonts and the leaderboard Worker. The r/aigamedev post had a score of 193 on Arctic Shift (observed; not a metric). Team size and location are not stated. The game was not played.
Development history
First shared on r/vibecoding with a link to the playable itch.io page.
DeveloperReddit (u/Jeb_the_killer)Shared on r/aigamedev; devlogs the same day add a new tutorial, a leaderboard fix, flight-stick support, arrow keys and an Arcade option.
Devlog: new tutorial, free flight and fixes.
Observeditch.io
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.
itch.io
Free in the browser (HTML5). Gamepad or joystick strongly recommended; keyboard, mouse, flight sticks, touch and tilt also work. Optional support payments are accepted.
Not publicly available: Gross revenue.
Reviews & rankings
Not yet reviewed by our editors.
Sources
| Source | Type | Published | Accessed |
|---|---|---|---|
| MACH RUN (r/vibecoding) Reddit (u/Jeb_the_killer) | Social post | Sep 27, 2026 | Nov 3, 2026 |
| MACH RUN - Built by opus 5.5 in essentially one prompt. (r/aigamedev) Reddit (u/Jeb_the_killer) | Social post | Oct 2, 2026 | Nov 3, 2026 |
| MACH RUN by JebKJ21 itch.io | Store page | Not confirmed | Nov 3, 2026 |
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