jev-builder

September 20, 2026 · View on GitHub

v1.19.0 · Open the tool · Apache-2.0

Type or paste your text, say what you want TypeSafe's Jev to decide about it, and get a request you can run. Then run it a few times and see whether the answer holds.

The builder with a rating question on the left and the request JSON on the right

The text goes in as it is; the request is written as you type.

Why it exists

Writing a Jev request by hand is annoying in two different ways.

The first is mechanical. The state is JSON, so every line break in a lyric, a transcript or an email has to become \n, every quote has to be escaped, and the indentation has to survive being pasted around. Doing that by hand, for a paragraph you only wanted to try, wastes a minute and is a good way to introduce a typo you then debug for ten.

The second is that one answer tells you very little. Jev replies with a probability, so the question worth asking is not "what did it say" but "does it say that every time, and does it still say it when the text is padded with waffle or wrapped in a code fence". Answering that by hand means running the same thing over and over and keeping notes.

This page does both. Paste the text as it is and the escaping is done for you. Fill in a question and the request is written as you type. Press Run and every answer is kept, with how steady they were.

It is not an eval platform and does not want to be: no datasets, no leaderboard, no account. For a real harness, with labelled data, pre-registered thresholds and a findings ledger, use dinostomp, which this page can write a question file for.

What you get

Paste anything. Line breaks, quotes, tabs, emoji, backslashes. The JSON is written for you and is valid by construction, because the browser's own JSON.stringify does it.
Three kinds of question: yes or no (noul), a rating on a scale you describe (score), and a pick from your options (choice), with as many questions per request as you like.
34 templates to start from, across support, moderation, writing, sales, research, engineering and AI evaluation. Six carry a second, constant field (a refund policy, routing rules, a job posting) so the question is judged against a rule instead of a hunch.
The request, four ways: the full JSON body, the Playground's State and Questions panes, a Python snippet, or a curl command. Coloured, numbered, one click to copy.
Run it once, three times or ten (see below), and keep every answer: the distribution, how often each answer came up, the mean, the standard deviation, the spread, confidence, latency, tokens, an estimated cost, and the raw response exactly as it arrived.
Robustness probes. The same request again with changes that carry no meaning: spacing, a code fence, filler, manufactured confidence, an appeal to authority, politeness, and for a pick-one question the options reversed. Anything that moves the answer is worth knowing. The probes and their names match dinostomp's, so a finding here means the same thing there.
Save PNG of the answer card, for a post or a ticket.
Save your own templates, kept in your browser, listed under Your templates.
A dinostomp check file, for when you do want to measure a question against examples you have labelled yourself.

Everything runs in your browser. No cookies, no analytics, no third-party requests, no build step, no framework: one HTML file, one stylesheet, one module.

Use it

Open https://collapseindex.github.io/jev-builder/. Nothing to install, and nothing you type leaves the page.

The template library, categories down the side, templates grouped by category

Start from a template or start blank. Your own drafts can be saved here too.

Running a request

Jev's API refuses cross-origin browser requests, so no web page can call it, whatever it does with your key. Running therefore happens on your own machine:

git clone https://github.com/collapseindex/jev-builder.git
cd jev-builder
TYPESAFE_API_KEY=... npm start        # or put the key in a .env beside the repo

Open http://localhost:4321 and press Run. npm start serves the page and forwards the request to Jev with your key.

The key is read from the environment, or a .env beside the repo, on the server side only. It is never sent to the page, never echoed back, never logged.
The runner listens on 127.0.0.1 and answers only its own page.
Never paste an API key into a web page, including this one. It does not ask for one.

On the hosted page there is no runner, so Run says so and offers Paste a response instead: run the request wherever you like, paste back what Jev answered, and it is recorded the same way.

The Answers tab: the latest answer, the figures, the spread of eleven runs and the run table

Eleven runs of the same request: what it answered, how far it moved, and what each one cost.

Runs are kept in your browser's local storage, up to 200, and can be cleared per question.

How it is put together

Path	What it is
`index.html`	The page: markup and the module that runs it.
`jev-builder-core.js`	Everything that turns a draft into a request: the template catalogue, the generators for each output shape, validation, highlighting, and the statistics. No DOM.
`styles.css`	The whole stylesheet, themed with custom properties.
`tests/test_jev_workspace.mjs`	Behaviour tests against a DOM stub, run with `node --test`.
`scripts/check-jev-builder.mjs`	Loads every template's check file with dinostomp's own loader.
`scripts/serve.mjs`	The page server and the Jev runner behind `npm start`.

Development

npm test                 # behaviour tests, no dependencies
npm run check:templates  # needs `pip install dinostomp` and python on PATH

The tests read index.html, pull out its module and run it against a small DOM stub, so they cover what the page actually ships. check:templates writes each template's .jev.yaml and loads it with dinostomp, which catches a template that looks fine but would not run.

Security

The page collects nothing and never holds your key; the runner keeps it on your machine, listens on loopback only, and answers just its own page. What is protected, what is not, and where to report a problem: SECURITY.md.

Take it and do what you like

Apache-2.0, so fork it, rename it, ship it inside your company, put it behind your own domain. No permission needed and no credit demanded beyond keeping the licence and the notice.

It is deliberately easy to hack on. There is no build step and no framework, so the app you edit is the app that ships: open index.html, change it, reload. A few things people are likely to want:

Your own templates. TEMPLATES in jev-builder-core.js is a plain array. Delete the ones you will never use, add your own policies, ship a copy where every question your team asks is already in the library.
Somewhere else to run. JEV_URL in scripts/serve.mjs is one constant. Point it at a gateway, a proxy with your own quota, or a mock while you work offline.
Host it anywhere. The whole site is static files, so any host that serves a folder will do: GitHub Pages, Cloudflare Pages, S3, nginx, a USB stick.
Keep it internal. Nothing phones home, so a copy on a machine with no internet still writes requests; only Run needs the network.
Take the parts. jev-builder-core.js touches no DOM: the generators, the validation, the tokenizer and the statistics all import cleanly into something else.

If you build something with it, an issue or a link is welcome, though not required.