jevcompat
48-requirement spec and conformance suite for Jev-compatible servers, with a normalising proxy; shows confidence is not portable.
Overview
jevcompat defines what Jev-compatible means for servers implementing TypeSafe's System One API. SPEC.md lists 48 numbered, testable requirements, each marked MUST or SHOULD and tied to its official source, and resolves eight places where TypeSafe's docs, OpenAPI file and SDKs disagree. Rules include Choice probabilities keyed by option and summing to one, Score equal to the probability-weighted sum, 2 to 255 options, error shapes, and answers that stay put when question ids or order change. jevcompat test runs the spec against any server and shows the request and bytes behind every failure; jevcompat proxy puts a conforming API in front of a non-conforming server, fixing what it can and loudly refusing what it cannot. A reference mock breaks each rule on purpose, and a GitHub Action is provided.
Its key finding is that confidence is not portable: open servers compute it four different ways. Applied to the same 204 recorded answers at a 0.9 threshold, TypeSafe's formula auto-accepts 58% while Laya's accepts 30%, so a threshold tuned on Jev silently changes automation rates elsewhere. Of the eight most-starred open servers tested, Kev and decider were conformant; others failed on issues such as rejecting many choice options or one-sided Noul criteria.
What the decision model decides
| Type | Question | Answers |
|---|---|---|
| Other | Does this server's /v1/systemone behaviour satisfy each of 48 spec requirements? | — |
How it works
- Run jevcompat test against a server URL
- Each requirement is exercised with crafted requests
- Report failures with the triggering request and bytes
- Optionally run the proxy to normalise responses and recompute confidence
Strengths
- Clear, sourced definition of compatibility
- Shows confidence formulas differ across servers
- Normalising proxy and GitHub Action
Caveats
- Spec reflects documentation as of its writing
- Proxy cannot fix every incompatibility
Getting started
uvx jevcompat test http://localhost:8000At a glance
- Type
- CLI
- Status
- beta
- Language
- Python
- Runtime
- CLI / proxy
- Has code
- yes
- Has tests
- yes
Use cases and integrations
How curated lists describe it
Interoperability: a 48-requirement spec of the `POST /v1/systemone` wire contract, each rule citing TypeSafe's docs, OpenAPI file or SDKs, and a suite that checks any Jev-compatible server against it (`Choice` probabilities keyed by option and summing to 1, `Score` equal to Σ i·p, 2–255 options, error shapes, answers that stay put when question ids or order change), finding 2 of the 8 most-starred open ports conformant, with a reference mock that breaks each rule on purpose and a proxy that fixes what can be fixed.
yibie/awesome-jevA testable spec and conformance suite for Jev-compatible (TypeSafe System One) API servers, with a normalising proxy, a reference mock and a GitHub Action.
hellogumbo/awesome-jev
Frequently asked questions
Which open servers were conformant?
Kev and decider among the eight most-starred tested on 2026-09-24.
Why does confidence portability matter?
A 0.9 threshold accepted 58% of answers under TypeSafe's formula but 30% under Laya's on the same data.
Can it fix a non-conforming server?
The proxy fixes what it can, such as recomputing confidence, and refuses the rest.
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