Jev is a "System One" model: instead of generating prose, it judges shared state against typed questions and returns choices, scores, and probabilities your code can branch on. That makes it a good fit for classification, routing, rubric scoring, and automated verification — and a poor fit for writing text, which it cannot do.

jev-cli eval -s "The support agent issued a full refund of \$40 and apologized." -q '{
  "refunded": {"type": "boolean", "instructions": "Was a refund issued?"},
  "tone":     {"type": "choice",  "instructions": "What tone did the agent use?",
               "criteria": {"warm": "friendly and personal", "curt": "terse or dismissive"}},
  "quality":  {"type": "score",   "instructions": "Rate how well this was handled.",
               "criteria": ["poor", "acceptable", "excellent"]}
}'

{
  "refunded": { "type": "boolean", "probability": 0.99 },
  "tone": { "type": "choice", "choice": "warm", "probabilities": { "curt": 0.02, "warm": 0.98 } },
  "quality": { "type": "score", "score": 1.78, "probabilities": { "0": 0, "1": 0.22, "2": 0.78 } }
}

Install

bun install -g @jtsang/jev-cli   # or: npm install -g @jtsang/jev-cli

The published binary runs on Node 22+ or Bun.

Set up

Get a key from the TypeSafe AI dashboard, then:

jev-cli config init
jev-cli config set providers.jev.apiKey <your-key>
jev-cli doctor

The default provider is jev, which calls TypeSafe AI's API directly. If you would rather route through the Vercel AI Gateway, switch to it:

jev-cli config set provider vercel
jev-cli config set providers.vercel.apiKey <your-gateway-key>

doctor sends one tiny evaluation to confirm the key and model actually work. Use --offline to check the configuration without a network call.

Usage

jev-cli eval  -s, --state <text>          -q, --questions <json>
              --state-file <path>            --questions-file <path>
              --state-json                   parse the state as JSON
              --provider <name>  --model <id>  --timeout <ms>
              --full     include usage, warnings, and provider metadata
              --compact  emit single-line JSON

jev-cli config init | path | list | get <key> | set <key> <value> | unset <key>
jev-cli doctor [--offline] [--provider <name>] [--model <id>]

Both inputs accept - to read from stdin, though only one may do so per invocation:

git diff | jev-cli eval --state-file - --questions-file ./checks.json

Question types

Every question needs instructions. Instructions and criteria descriptions may each be a string, a JSON object, or a JSON array.

Type	`criteria`	Answer shape
`boolean`	Optional `{"true": …, "false": …}`	`{"type":"boolean","probability":0.98}` — P(true), uncalibrated
`choice`	Required. Option name → description (or `null`)	`{"type":"choice","choice":"warm","probabilities":{…}}`
`score`	Required. Array of ≥2 levels, lowest first	`{"type":"score","score":1.83,"probabilities":{…}}`

A score is a fractional position in [0, levels-1] — the probability-weighted mean, not an index. Confidence for choice and score answers is reported under providerMetadata when you pass --full: at jev.answers.<id>.confidence on the jev provider, and at typesafe.confidence through the gateway.

Questions are evaluated in parallel and in isolation against the same state, so adding questions costs almost nothing — but each one must stand on its own. Keep them atomic and combine the results in your own code.

Configuration

~/.jev-cli/config.yaml, written with 0600 permissions. Override the directory with JEV_CLI_HOME.

provider: jev
providers:
  jev:
    apiKey: "..."
    model: jev-latest
    # baseURL: https://api.typesafe.ai/v1
  vercel:
    apiKey: "vck_..."
    model: typesafe-ai/jev
    # baseURL: https://ai-gateway.vercel.sh/v4/ai

Only the active provider's settings are read, so both can live in the file at once.

`provider`	Default model	Key from	Environment fallback
`jev` (default)	`jev-latest`	TypeSafe AI	`JEV_CLI_API_KEY`, `TYPESAFE_API_KEY`, `TYPESAFE_AI_API_KEY`
`vercel`	`typesafe-ai/jev`	Vercel AI Gateway	`JEV_CLI_API_KEY`, `AI_GATEWAY_API_KEY`

Precedence is CLI flag > environment > config file — handy in CI, where you can skip the config file entirely.

Switch with jev-cli config set provider <name>, or per call with --provider <name>. Note that JEV_CLI_API_KEY applies to whichever provider is active: if you keep both configured, set the provider-specific variables instead, or the same key gets sent to both.

On the jev provider, model takes jev-latest, jev-preview, or a pinned release such as jev-1.13.0. Pin the version once you have calibrated confidence thresholds, since the aliases move when a release ships.

Keys are masked in config list output unless you pass --show-secrets.

Exit codes

eval prints errors to stderr as JSON, leaving stdout for results alone.

Code	Meaning
`0`	Success
`1`	Provider or network failure
`2`	Bad usage or invalid questions
`3`	Missing or rejected credentials

Agent skill

This package ships skills/use-jev-cli, a skill that teaches coding agents when and how to use jev-cli.

Development

bun install
bun test            # unit + CLI end-to-end tests
bun run typecheck
bun run build       # bundles to dist/cli.js for Node
bun link            # install the local build as a global jev-cli

Releases are documented in RELEASING.md.