The Dark Stair: We Asked Fable 5 to One-Shot a Game. It Did.

⚔ Play The Dark Stair — Free Runs in your browser. Nothing to install, nothing to sign up for.

One evening we started an agent running Claude's Fable 5 with a single prompt:

"One-shot an app. Providing me anything other than a final, polished, flawless product is a fail. I want it to be some kind of game. Be bold — this should be complicated, not something like pong or galaga."

Thus, The Dark Stair was born.

v1: no bugs. A complete, playable roguelike on the first pass — procedural dungeons, combat, items, a boss. v2: no bugs. At that point we gave it guidelines for sending subagents to playtest the game for balance and creativity, told it to iterate until morning, and went to bed.

v3 through v7 happened overnight. Along the way, the agent used our GCP auth to generate voice lines, wrote Python to generate its sprites, built scenes in Blender for the cutscene art, and added ambient music of its own accord. In the morning: still no bugs.

Maybe you can help us find one.

The Game

The Dark Stair is a classic turn-based roguelike, compressed into a tight browser session:

Six procedurally generated floors — every run is a different dungeon, with themed floors, shops, shrines, and secrets.
Three classes — warrior, rogue, and mage, each with their own starting kit, field of vision, and playstyle.
Three difficulties — from Adventurer ("a gentler dark") to Nightmare ("the dark usually wins").
A seeded daily challenge — one dungeon, the same for everyone, every day. Compare your run.
Echoes — die, and a future run may find your body where you fell, along with a share of your gold.
The Lich — six floors below, stirring. Conduct bonuses reward winning without potions or merchant deals.

It saves your run locally, so you can close the tab mid-dungeon and pick up where you left off.

Technically, it's deliberately old-school: vanilla JavaScript, zero frameworks, zero dependencies, rendered on a canvas, weighing about 1.8 MB including audio. It loads in under a second and runs on anything with a browser — including your phone.

The Honest Footnote

Is Fable 5 insane? Yes. Is the model the whole story? No. The agent was running inside our harness / MCP / hooks ecosystem — the same scaffolding we build for clients: tool access, knowledge retrieval, testing discipline, subagent orchestration, and review gates. A frontier model with a single prompt got the spark; the ecosystem is what let it run unattended all night and come back with v7 instead of a stack trace.

1One prompt, full autonomy. The agent owned architecture, art, audio, and balance decisions end-to-end — including spawning its own playtest subagents overnight.

2Real tools, not toys. It reached for GCP text-to-speech for voice lines, Python for sprite generation, and Blender for scene art — because the harness gives agents real tool access.

3And it still runs the show. Today the same ecosystem operates the game in production: the "Whisper to the Keeper" feedback widget feeds the agents' task queue, gameplay telemetry informs balance, and agents watch traffic and scaling.

The point: if one prompt plus our agent ecosystem can produce a complete game overnight, imagine it pointed at your internal tools, integrations, and workflows. The dungeon is the demo.

Go Face the Lich

Enough process talk. The stairs are right there.

⚔ Descend The Dark Stair Tip: start as the warrior on Veteran. Press D on the title screen for today's daily challenge.

If you make it to the Lich — or especially if you don't — tell us about it through the whisper widget in the corner of the game. Every note lands in front of the team (human and otherwise).

Want the pipeline that built this pointed at your business instead of a dungeon? Book a consultation.

We Asked Fable 5 to One-Shot a Game. It Did.

The Game

The Honest Footnote

Go Face the Lich

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