Independent developer guide · updated September 2026

The Jev model,
explained for builders.

Jev turns messy software state into typed decisions your code can branch on: a choice, a score, or a calibrated yes/no probability.

choice route score rank noul gate
software state typed output
state

"The customer has been billed twice and wants a refund today."

Jev / System One
decision
choicebilling0.98
noulescalate0.92
Live shape

Messy text in.
Typed decision out.

Use this small example to understand the contract. The real value is not another chat window; it is a fast decision your application can safely consume.

POST /v1/systemone live example
state0c
questions3 typed decisions
choicetopicprimary issue
scoreseverity0 to 3 risk level
noulescalateyes/no probability
Typed output will appear here.
Where it fits

Put the decision layer
between intent and action.

Jev is most interesting when a workflow already has an LLM, an API, or an agent, but needs a small reliable branch before the next step.

See all use cases
Start with a branch

Find the fuzzy if
your agent was missing.

Open API examples