What does Jev actually decide, and what stays in code?

The engines keep the rules: Hundred's movement, needs, food, work, theft, help and fights, and Shogi's legal moves, drops, promotion, check and mate. Jev only answers what this person should do next, and in Shogi its reply is picked from the engine's legal USI moves, so it cannot invent an illegal one. A Jev timeout or error falls back to local rules.

Will leaving Hundred on Jev run up my bill?

It will, which is why Hundred ships on local rules and only calls Jev when you set DECISION_PROVIDER=jev. Shogi is the opposite default: SHOGI_PROVIDER is jev whenever a key exists, and setting it to rules forces local replies. pnpm test:jev is the cheap way to confirm a key before pointing a whole town at it.

Can I inspect past decisions without paying for more calls?

Yes. Recorded Hundred decisions land in a run directory named by timestamp and seed, and pnpm replay with that path re-runs them while never calling the Jev API. Hundred also has a replay provider alongside rules and jev in its decision provider list, which is the cheap path for debugging behaviour.

Do I need Nix or WSL2 to get it running?

No. git clone, pnpm install and pnpm dev is the quick start, needs no API key, and opens the lab hub on 127.0.0.1:5173 with each product on its own port. Nix is there for a pinned, reproducible environment, and the WSL2 advice is about keeping dependency installs per OS rather than a requirement.

What are the default provider settings for each product?

Hundred ships on local Rules and only calls Jev when you set DECISION_PROVIDER=jev. Jev Shogi defaults to SHOGI_PROVIDER=jev whenever a key exists, and setting it to rules forces local replies. A Jev timeout or error falls back to rules in both.

What is the cheap way to confirm my Jev key works?

pnpm test:jev makes a live test call to confirm the key before pointing a whole town at it. That matters because Hundred on Jev spends credits per decision, and a hundred NPCs add up.

What stack are the two products built on?

TypeScript, pnpm workspaces, Vite, React 19, PixiJS 8, Hono, Zod, Vitest, Oxlint and Oxfmt. pnpm check validates the workspace, and an optional Nix flake pins Nixpkgs and supplies Node 24 with a Corepack-backed pnpm.

CommunityJev Demos & Experiments

Jev Lab — jammaru

Two TypeScript monorepo products that keep the rules in the engine and ask Jev exactly one question: what should this person or this shogi side do next. Hundred runs a hundred NPCs with hunger, money, jobs, relationships and memories; Jev Shogi picks Gote's reply from engine-legal USI moves.

See highlights

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Stars: 7
Language: TypeScript
License: MIT
Published by: Community
Author: jammaru
Last verified: Oct 2026

jammaru/jev-lab

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100 AI NPCs live in a tiny town. Jev chooses the next action; the world writes the story.

Forks: 1
Last pushed: Updated Oct 2026

Repo stats from the GitHub API, cached Oct 2026.

About this project

Use cases for Jev, TypeSafe’s System One model. Jev only answers the next choice. Engines keep the rules. Open ` No API key is required. Products start in Rules mode. pnpm dev:hundred and pnpm dev:shogi start one product at a time. One hundred NPCs live in a tiny town with hunger, money, jobs, relationships, and memories. Jev only answers what should this person do next?

Quoted from the project's README. Read the full README.

Tagscommunity jevbest catalog-import awesomejev

Works forJev for Classification Jev for Routing

Used inJev for Software & DevTools

Languages: TypeScript

Highlights

Jev never receives a whole world or a whole game tree; each request is compact state plus the currently legal options.
Both products start in local Rules mode with no API key, and both fall back to rules when Jev times out or errors.
Hundred stays on local rules until DECISION_PROVIDER is set to jev, which is the moment the town starts spending credits.
pnpm replay re-runs recorded Hundred decisions from a run directory without ever calling the Jev API.

Watch out

Nix is optional but documented in detail: the flake pins Nixpkgs and supplies Node 24 with a Corepack pnpm, and Windows users are told to work inside WSL2 and keep node_modules separate per OS. The Jev path is opt-in per product and costs credits per decision, so a hundred NPCs on Jev adds up, and a timeout silently reverts to rules, which is easy to mistake for the model having decided. Browser tests on Ubuntu or WSL need Chromium installed once with its OS dependencies. Copy reviewed against the repository README on 2026-10-04, not from running it.

Questions about this entry

Short answers drawn from the linked project or page.

Other listings of this project

Forks and copies of this project in the directory. This entry is the canonical one.

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