Tic Tac Jev

Tic-tac-toe, but every move for one side comes from Jev, a System One Model built for fast, structured decisions — unstructured state in, typed probabilistic decisions out.

Each Jev move is a structured, typed decision, not free-form text. The backend hands Jev the board as a Choice question — one labeled criterion per open cell ("center", "top-right corner", etc.) — and gets back a chosen cell, a confidence score, and a full calibrated probability distribution over every option it weighed. The frontend surfaces that reasoning move by move: expand any Jev entry in the move log to see the probability bar for every cell it considered before committing.

It's a small decision space — 9 cells, at most 8 legal moves at any turn — which makes Jev's reasoning easy to watch end to end, move by move.

How it works

• POST /games creates a game with a chosen human symbol and who goes first.
• POST /games/{id}/moves submits a human move, then — if the game isn't over — asks Jev for its move.
• On each Jev turn, JevClient.choose_move (backend/app/jev_client.py) builds a Choice question whose criteria are only the currently-empty cells, sends the board as natural-language state, and gets back a ChoiceAnswer: the chosen cell, its confidence, and the probability Jev assigned to every candidate cell.
• The full move history — including Jev's confidence and per-cell probabilities — is kept on the game state and returned to the frontend, which renders it live in the move log.

Project layout

backend/   FastAPI service: game state, rules, and the Jev client
frontend/  React + Vite UI: board, setup form, move log with probability bars
assets/    Screenshots and a recording of the app in use

Backend setup

Requires Python 3.12+, uv, and a Jev API key.

cd backend
cp .env.example .env   # then set JEV_KEY to your key
uv sync
uv run uvicorn app.main:app --reload

The API listens on http://localhost:8000 and only allows CORS from http://localhost:5173 (the Vite dev server).

Run the backend tests:

uv run pytest

Frontend setup

Requires Node.js.

cd frontend
npm install
npm run dev

The dev server runs on http://localhost:5173 and talks to the backend at http://localhost:8000 by default (override with VITE_API_BASE_URL).

Run the frontend tests:

npm test

Configuration

The backend reads settings from backend/.env (see backend/.env.example):

Variable	Required	Description
JEV_KEY	yes	API key for Jev
JEV_BASE_URL	no	Override the default Jev API base URL
JEV_DEFAULT_MODEL	no	Override the default Jev model
JEV_TIMEOUT	no	Request timeout in seconds (default 10.0)