# Jev & TypeSafe

> For builders new to System One. Jev takes structured state and typed questions, then returns probabilities your code can threshold before you browse SDKs.

## Answer

Jev is TypeSafe's System One decision model for software teams who need a label, a score, or a yes-or-no gate: send structured state and typed questions, and the API returns probabilities your code can threshold.

## What is Jev?

Jev is TypeSafe's flagship System One model. You send structured state and typed questions; the API returns discrete answers with per-option probabilities and confidence scores. Your application code applies thresholds and executes side effects.

## Where to start

Read the introduction at typesafe.ai, follow the quick start on docs.typesafe.ai, and poke the browser playground. For production, install @typesafe-ai/sdk or typesafe-sdk on Python and call POST /v1/systemone.

## Relationship to this directory

jev.aitools.fyi is an independent curated directory by aitools.fyi. Listings link to third-party projects; only official TypeSafe properties are authored by TypeSafe AI.

## Choice, Score, and Noul

Choice picks one label from a fixed set with explicit probabilities. Score returns a numeric rating with uncertainty you can map to bands. Noul answers structured true or false style questions with confidence. Compose these primitives instead of prompting for free text and regex-parsing the reply.

## Request shape in practice

Production clients send JSON state plus an array of typed questions in one POST to /v1/systemone. The response carries aligned answers with per-question confidence. Your service layer applies thresholds, logs decisions, and triggers side effects. There is no hidden chain-of-thought stream to consume.

## When Jev is the wrong tool

Skip Jev when you need long-form copy, open-ended brainstorming, or narrative reasoning. Reach for an LLM or a template engine there. Many teams pair both: Jev for gates and routing, generative models for user-visible language.

## FAQ

### What is Jev?

Jev is TypeSafe's flagship System One model. You send structured state and typed questions, and the API returns discrete answers with per-option probabilities and confidence scores.

### Will Jev write the email?

Skip Jev when you need long-form copy, open-ended brainstorming, or narrative reasoning. Many teams pair both: Jev for gates and routing, generative models for user-visible language.

### Are these the official TypeSafe docs?

jev.aitools.fyi is an independent curated directory by aitools.fyi. Read the introduction at typesafe.ai and follow the quick start on docs.typesafe.ai.

Directory copy checked 2026-10-17. This directory is independent of TypeSafe AI unless a listing says it is official.
Canonical: https://jev.aitools.fyi/learn/jev-typesafe
Markdown: https://jev.aitools.fyi/learn/jev-typesafe.md