CODEX MORTIS
A survivors-like necromancy deckbuilder whose Steam page says AI wrote all of its code.
Links go to the official store or developer page. Last verified Nov 3, 2026.
Where to play
Every platform this game is on. Links are checked against official sources; we never host or mirror games.
- View on SteamSteamReleased · Full 1.0 release on 24 Sep 2026 after Early Access from 26 Mar 2026. Publisher: CRUNCHFEST.$3.99
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Desktop · Steam
About CODEX MORTIS
A survivors-like bullet-hell roguelite with deckbuilding, mutating spells and ten schools of dark magic, with local and online co-op for up to four players. The developer's AI disclosure on Steam says AI was used for the entire code of the game, as well as its text, art, sounds and music. A Japanese press report, citing the developer's December 2025 Reddit post, says the code was written with Claude Code and the art made with ChatGPT. It is developed by GROLAF, published by CRUNCHFEST, and sold on Steam for Windows and Linux.
Screenshots and art
CODEX MORTIS key art · Steam store artwork
How it was built
Partially verifiedA Japanese press report, citing the developer's December 2025 Reddit post announcing the demo, says the code was vibe-coded with Claude Code, mostly with Claude Opus 4.1 and 4.5, and that the character animation is a shader Claude Code wrote. The developer's Steam AI disclosure says AI wrote the entire code, but does not name the tool.
- DeveloperSteam AI Generated Content Disclosure: AI used for the entire code, text, art, sounds and music. No tool named. — Steam
- DeveloperReport on the Steam demo and its claim to be made 100% through AI; does not name the coding tool. — PC Gamer
ChatGPT, used in its normal chat interface rather than the image API, made the art, according to a Japanese press report citing the developer. On the Steam forum the developer writes that ChatGPT was the best tool at keeping a consistent style over time.
- DeveloperDeveloper names ChatGPT as the best tool for stylistic consistency. — Steam Community
The developer says a first playable prototype existed within days, then the code was restructured around an entity-component system; human testers found and fixed about 100 bugs over several months. No commercial engine.
- Engine / framework
- No engine (PixiJS rendering, bitECS, Electron)
- Languages
- TypeScript
- Team size
- Not disclosed
- Development time
- Not disclosed
- Development cost
- Not disclosed
- AI-written code
- Not disclosed
“AI is used for entire code of the game, text, arts, sounds and music.”Verification notes: Release date, price, platforms, developer, publisher and the AI disclosure checked on the Steam store and store API; Early Access and 1.0 dates checked in the developer's Steam announcements. The Claude Code and model attribution comes from press quoting the developer's Reddit post, which we could not open directly. Press also describes GROLAF as a solo developer; not confirmed in a primary source.
Development history
- December 2025
Free demo released on Steam; the developer explains the AI workflow on the Steam forum.
Released in Early Access on Steam.
Version 1.0 leaves Early Access, adding online co-op for up to four players and five more schools of magic for ten in total. Press reports a roughly 15-minute documentary by the developer on how the game was made was released with it.
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.
Steam
US$3.99 on the Steam store (US region, no discount) when checked. Windows and SteamOS + Linux.
Not publicly available: Concurrent players, Steam reviews, Positive Steam reviews, Estimated owners, Gross revenue.
Sales & revenue (all platforms)
Reviews & rankings
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Sources
| Source | Type | Published | Accessed |
|---|---|---|---|
| CODEX MORTIS on Steam Steam | Store page | Not confirmed | Nov 3, 2026 |
| Codex Mortis is Available Now! Steam (CRUNCHFEST & GROLAF) | Devlog | Mar 26, 2026 | Nov 3, 2026 |
| Codex Mortis 1.0 is OUT NOW! Online co-op, ten schools of magic and 31 heroes Steam (CRUNCHFEST & GROLAF) | Devlog | Sep 24, 2026 | Nov 3, 2026 |
| Developer's answer about how the game was made Steam Community | Social post | Dec 12, 2025 | Nov 3, 2026 |
| 『CODEX MORTIS』正式版配信|Claude Codeで「100％AI開発」したゲームは早期アクセス半年で何を作り直したか gaming-st.com · Japanese | Press | Sep 27, 2026 | Nov 3, 2026 |
| This roguelite claims to have the dubious honor of being 'the world's first fully playable game created 100% through AI' in a milestone for slop everywhere PC Gamer | Press | Not confirmed | Nov 3, 2026 |
