Ran @typesafeai's Jev against an existing classifier eval that previously used Gemini 2.5 Flash Lite. It won both on quality (saturated the eval) and speed (6x)
Score
Rate content against 2 to 10 ordered levels. Returns a probability-weighted score that can land between levels, per-level probabilities, and confidence, with the arithmetic left to code.
- Category
- Practices & Patterns
- Published by
- TypeSafe AI
- Author
- —
- Added
- 2026-09-20
Tagsofficialprimitivesscoreconfidenceevaluation
Highlights
- Levels are numbered by array position from 0; the model sees the descriptions, not the numbers.
- The score is each level number times its probability: 0x0.0 + 1x0.57 + 2x0.43 = 1.43.
- Levels are judged separately, so describing one level as worse than another adds no signal.
- Confidence 1.0 means every ounce of probability sits on a single level.
Quickstart
python
"bug_severity": Score(
instructions="How severe is the reported issue?",
criteria=[
"Cosmetic; no impact to functionality",
"Broken or degraded feature, but workaround exists",
"Blocking issue; no workaround exists",
],
)Watch out
A confident answer is not a correct answer, and Score levels are poor at exact numeric calibration, so threshold in code rather than reading the score as a measurement.
More like this
A maintained list of jev-1.13's known failure modes, literal reading, unreliable counting, dates as text, indirection, context rot, and contradictory criteria, each with a guardrail.
Practices & Patterns#official#docs#evaluation
Official
Pick one option from a set you define. Returns the option, the full probability distribution, and 0-1 confidence, with up to 255 options and parallel questions that barely add latency.
Practices & Patterns#official#primitives#choice
Official
The yes/no primitive: one probability from 0 to 1, where the value is the answer and no separate confidence is needed. True and false criteria pin down subtle boundaries.
Practices & Patterns#official#primitives#noul
Official
From the community
Posts from builders shipping with Jev right now.
Beating Gemini Flash Lite on an eval
Browser Use Ultrafast, powered by Jev
Breaking: Browser Use + Jev = Ultrafast ⚡ Findings flights took 7s and cost only $0.0039 🤯 > new action space every step > DOM state space > small LLM fallback to type (this video is at 1x speed btw) Built a tiny open source browser agent. try it below ↓

