jev-repl

How we reviewed this: we ran its 157 tests in Docker and drove check, json, cost and run end to end against a local stand-in, capturing the request. We made no Jev calls.

What it does

jev-repl, by Andrei Oprisan, is a terminal REPL and a zero-dependency TypeScript client for System One. You write a question on one line — :noul is_threat The message threatens violence | yes: … | no: … — press enter, and get bars. A .jev sketch file holds a page of them, and four headless subcommands take it from there: check validates, json prints the request, cost estimates locally without calling anything, and run calls.

Then there’s a web build of the same thing, where a share link carries the page in the URL fragment and, as the UI says, “the page travels in it, the key never does”. We read share.ts; it’s true.

The engineering

This is the most solid project in this batch and it isn’t close. 157 tests across eight files, all passing. CI runs lint, typecheck, build and tests on Node 22 and 24, plus a separate job that smoke-tests the built artifact on 18.17 and 20 because the package claims to support them and the test runner doesn’t. Zero runtime dependencies.

The details that usually go missing are all present: the answer shape is validated against the question, the API key is checked for header-injection characters before use, URLs are redacted in errors, sensitive headers are listed and stripped, the retry has jitter and a 30-second total budget checked before each sleep, and the sleep timer is unref’d so it can’t hold the process open. In the REPL, a key typed at the prompt is neither echoed nor written to history — there’s a comment saying so, and it’s accurate. In the browser the key is not stored unless you ask, and every screen has a forget button.

We went looking for a bug and didn’t find one.

Two things to know

It sends a runtime fingerprint header — node v24.21.0 (linux; x64) from the CLI. The browser build sends only "browser", with a comment explaining the choice: “Nothing about the browser but that it is one.” Deliberate, and worth knowing.

And the web version lets you point the base URL anywhere, storing it in localStorage and sending your key there as a bearer token. That’s the feature working as intended; it’s still your key going to a host you typed.

Verdict

If you’re designing questions, start here: cost tells you the price before you spend it, json hands you the request, and the client underneath is good enough to keep.

Zero stars, and about half the commits are authored by the maintainer’s coding agent and merged through pull requests — which, on the evidence of the test suite and the CI matrix, is working.

For the same shaping job as an MCP tool, see jev-eval-mcp.

See how it compares with other tools in Best Jev tools, tested hands-on.

Review updated Sep 20, 2026. Numbers quoted from the project are its author's own; we don't publish our own measurements of Jev.