Jev Playground

A browser-only testbed for Jev, TypeSafe AI's decision model, running through the Vercel AI Gateway.

Live: https://jevplayground.terrydjony.com

Jev is not a chat model. You give it some state (a ticket, a transcript, a JSON record) and a set of typed questions; it answers all of them in one parallel pass with probabilities attached:

Question type	You define	You get back
boolean	instructions, optional true/false criteria	probability
choice	named options with descriptions	choice + probability per option
score	ordered levels, lowest to highest	interpolated score + probability per level

What the playground does

• Paste your AI Gateway API key, pick a preset (work or fun), press Evaluate
• Build boolean / choice / score questions against plain-text or JSON state
• See verdicts, probability bars, latency, token usage, and estimated cost
• Set an auto-accept threshold to see which answers would need human review
• Inspect the raw request and response, or copy an AI SDK / curl snippet
• Share a result as an image, or as a link that reopens the same setup

Your API key

There is no backend. The page calls https://ai-gateway.vercel.sh/v4/ai/evaluation-model directly from your browser. Your key is sent only there, is kept in memory unless you tick Remember (then it goes to localStorage), and is never included in shared images or links.

Get a key from the Vercel dashboard under AI Gateway → API Keys.

Run locally

It is a single static file with no build step:

npx serve public        # or: python3 -m http.server -d public 5173

Deploy

npx wrangler deploy     # Cloudflare Workers static assets, see wrangler.jsonc

How it talks to the gateway

Vercel documents evaluation models as AI SDK 7+ only (experimental_evaluate). This page makes the same HTTP call the @ai-sdk/gateway provider makes:

POST https://ai-gateway.vercel.sh/v4/ai/evaluation-model
Authorization: Bearer <key>
ai-gateway-protocol-version: 0.0.1
ai-gateway-auth-method: api-key
ai-model-id: typesafe-ai/jev

{ "state": ..., "questions": { ... } }

The SDK also sends an ai-evaluation-model-specification-version header. It is left out here because the gateway's CORS preflight does not allow it from browsers, and the endpoint works without it.