jevclient

Async Python client for TypeSafe Jev, the System One decision model. Jev answers typed questions about a state and returns values, so there is no text to parse.

import asyncio
from jevclient import JevClient, Noul, Choice, Score

async def main():
    async with JevClient("your-api-key") as jev:
        answers = await jev.ask(
            "The front door has been unlocked for 40 minutes and nobody is home.",
            {
                "warn": Noul("Should someone be warned about this?"),
                "area": Choice("Which area is this about?",
                               {"security": "Doors, locks, alarms",
                                "climate": "Heating and ventilation"}),
                "urgency": Score("How urgent is it?",
                                 ["Ignore", "Today", "Right now"]),
            },
        )
    print(answers["warn"].noul)          # 0.94
    print(answers["area"].choice)        # "security"
    print(answers["area"].probabilities) # {"security": 0.97, "climate": 0.03}
    print(answers["urgency"].score)      # 1.8, between "Today" and "Right now"

asyncio.run(main())

Three question types

A Noul carries no confidence, because the probability is the whole answer.

What one call costs

Every question in a call is evaluated in isolation against the same state, and the API answers them in parallel. Measured from the Netherlands on 2026-09-17:

Two things follow. Batching questions into one call is nearly free in time, so ask everything you want to know at once. It is not free in money: question text is billed as input tokens, roughly 38 for a short question, and output is billed at zero.

Those figures are first calls on a cold connection. Over 16 calls from the same place, a warm connection answered in 250 to 580 ms.

A choice takes 2 to 255 options and a score takes 2 to 10 levels. Both are checked locally, so a mistake costs no request.

Install

pip install jevclient

Requires Python 3.12 and aiohttp. Pass your own aiohttp.ClientSession if you have one, and the client will use it and leave closing it to you.

Another endpoint

base_url points the client at something other than https://api.typesafe.ai, and model names the model to ask for. The client appends /v1/systemone to the base URL, so a path in it is kept as a prefix.

An empty api_key sends no Authorization header, for an endpoint that asks for no credential:

JevClient("", base_url="http://gateway.local:8093", model="systemone-small")

Errors

JevAuthError (401), JevValidationError (422), JevRateLimitError (429, carries retry_after), JevOverloadedError (529) and JevConnectionError, all deriving from JevError. There is no internal retry loop, so the caller decides the policy.

A Choice with fewer than two options and a Score with fewer than two levels are refused locally, before a request is spent on a 422.

Not affiliated with TypeSafe

This is an independent client. See the TypeSafe docs for the API itself.