jev-harness
Deterministic-first 'System 1.5' gate for coding agents: triages test failures, breaks doom loops and governs effort, with optional Jev.
Overview
Jev Harness by ismaelsoilet is a token optimiser and decision gate for AI coding agents such as OpenCode, Claude Code, Cursor, Windsurf, Zed and Pi. It describes itself as a deterministic-first System 1.5 layer for the code-quality loop: triaging test failures (for example resolving missing dependencies or network flakiness without a frontier model), breaking circular doom loops, vetoing premature completion, governing reasoning effort and routing models. List summaries describe five semantic gates and a dependency-free local deterministic mode.
It is callable as a CLI, MCP server, git and CI hook, and typed SDKs in Python, TypeScript and Rust, and the README positions it against neighbouring tools (runtime supervisors, tool-call guards, context sieves, capability routers). A universal integration guide promises setup without an API key to start. Performance claims such as sub-millisecond triage come from the author. Documentation is in English and Portuguese. It is one of several projects named jev-harness.
What the decision model decides
| Type | Question | Answers |
|---|---|---|
| Choice | What kind of test failure is this (missing dependency, network flake, real bug...)?(inferred) | — |
| Yes / no | Is the agent stuck in a doom loop?(inferred) | — |
| Choice | What reasoning effort does this step need?(inferred) | — |
How it works
- Agent hits a test failure or loop
- Deterministic heuristics resolve trivial cases with zero tokens
- Escalate ambiguous cases to Jev semantic gates
- Gate completion, effort and routing
Strengths
- Works offline in deterministic mode
- Three language SDKs and MCP
- Clear scope relative to related tools
Caveats
- Performance claims are the author's
- Many agents listed; depth of each integration unclear
Getting started
See docs/AGENT_INTEGRATION_GUIDE.md for a two-minute setup without an API key.At a glance
- Type
- CLI
- Status
- beta
- Language
- Python
- Runtime
- CLI, MCP server, SDKs (Python, TypeScript, Rust)
- Has code
- yes
Use cases and integrations
How curated lists describe it
Developer tooling: System 1.5 quality gate and token optimizer for AI coding agents that triages test failures in < 500 µs to resolve missing dependencies without frontier LLMs, aborts circular doom loops, and modulates reasoning effort across Python, TypeScript, and Rust.
yibie/awesome-jevZero-dependency System One decision harness: 5 semantic gates saving frontier AI agent tokens on trivial errors & doom loops. Python + TypeScript + Rust. MCP-compatible.
hellogumbo/awesome-jevFive semantic gates in front of a frontier agent, for trivial errors and doom loops, with a dependency-free local deterministic mode. English and Portuguese. One of three projects on this list called jev-harness.
MrJev/awesome-jev
Frequently asked questions
What does it decide?
Test failure triage, doom-loop detection, completion veto and reasoning effort.
Do I need a Jev key to start?
No, a deterministic offline mode works without one.
Which runtimes are supported?
Python, TypeScript and Rust, plus CLI and MCP.
Related projects
Bash-native CLI that filters any stream by meaning with Jev, like grep for semantics, so an agent wakes only for lines that matter.
ProjectbetaTypeScriptMulti-agent orchestration layer for Claude Code with opt-in Jev hooks for fast judgment points, decision caching and egress controls.
PluginproductionTypeScriptnpm library that rate-limits, spend-caps, caches and redacts every Jev request made in a loop.
LibrarybetaJavaScriptLocal desktop pal that verifies what a coding agent really did, with optional Laya or Jev double-checks of unclear test results.
ProjectbetaTypeScriptSoftware-factory supervisor where Jev independently judges coding agents' completion, test sufficiency, progress and need for a human.
ProjectbetaPythonSecurity hook giving Codex, Copilot, Gemini, Cursor, pi, OpenCode and ACP an auto-mode-like guard via three Jev questions.
LibrarybetaTypeScript