Montanha: Zero Day
A cyberpunk 2D platformer in the browser, coded in a day with Claude Code.
Official site tiagovilasboas.github.io, verified Nov 3, 2026. Linked from the developer's own DEV post and from the README of his GitHub repository.
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.
- View on GitHubGitHubReleased · Source code (MIT); art all rights reservedFree
Source code repository, not a place to play.
GitHub
About Montanha: Zero Day
A side-scrolling 2D action platformer in the style of Mega Man X, set in a cyberpunk city. It runs in the browser on desktop and mobile, with touch controls, and installs as an offline web app. Developer Tiago Vilas Boas writes that Claude Opus 5.5, working through Claude Code, built the game in one day: about 2,700 lines of vanilla JavaScript across 24 files. The art was generated with separate AI image and video tools, and the source code is public under the MIT licence.
How it was built
VerifiedThe developer writes that Claude Opus 5.5, through Claude Code, wrote the game (about 2,700 lines of vanilla JavaScript in 24 files) in one day, and that Claude Code ran local tools such as Python, ffmpeg and git in the same session. The repository README credits "Claude Opus 5.5 (Cowork)". The art was generated separately through Artlist (Nano Banana 2 for images, Seedance for animation).
- DeveloperREADME: "Developed with the help of Claude Opus 5.5 (Cowork)." — GitHub
Built in one day with Claude Code, according to the developer. Code is vanilla JavaScript ES modules with no build step, drawn on an HTML5 Canvas, with a service worker for offline play. Music and sound effects are synthesized in the browser with WebAudio. Art and video were generated with Artlist tools.
- Engine / framework
- None (vanilla JavaScript, HTML5 Canvas)
- Languages
- JavaScript
- Team size
- Not disclosed
- Development time
- Not disclosed
- Development cost
- Not disclosed
- AI-written code
- Not disclosed
“Opus 5.5, through Claude Code, used about half of my daily allotment on the usage panel and shipped the game.”Verification notes: AI tool, model, code size and play link checked in the developer's DEV post and the repository README. The post shows "Oct 4" with no year; 2026 is inferred. The exact release date of the game is not stated.
Development history
The developer publishes his write-up on DEV; the game is already playable on GitHub Pages.
DeveloperDEV Community
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)
No public metrics recorded for this listing.
Not publicly available: Concurrent players (site), Monthly revenue, Gross revenue.
GitHub
No public metrics recorded for this listing.
Not publicly available: GitHub stars.
Sales & revenue (all platforms)
Browser game — there are no downloads to count.
Reviews & rankings
Not yet reviewed by our editors.
Prototype: your vote is kept only in this browser and is not counted anywhere.
Not currently ranked.
No player reviews yet.
Prototype: reviews are stored in your browser only and are not published or sent to a server. Reviews are shown in the language they were written in.
Sources
| Source | Type | Published | Accessed |
|---|---|---|---|
| I Built a Full PWA Game in One Day with Claude Opus 5.5 and Claude Code (Here Is the Real Token Cost & Harness Setup) DEV Community | Devlog | Oct 4, 2026 | Nov 3, 2026 |
| tiagovilasboas/montanha-zero-day GitHub | Repository | Not confirmed | Nov 3, 2026 |
