How is this different from just wiring up a Playwright MCP server?

You keep writing your own locators. Semantic matchers extend Playwright's existing expect, so toSemanticallyMatch sits alongside the assertions you already have, and an exact expected value needs no model configuration at all. The decision backend only chooses among candidates you supply; it does not generate selectors or executable JavaScript.

What happens if my playwright-core version drifts?

It is a peer dependency, not a bundled copy, so npm and pnpm install it for you while Yarn Berry needs it added explicitly. The supported range is >=1.62.0 <2 and an older copy is rejected with a CONFIG error. If your project sits on an older @playwright/test than the newest release, pin playwright-core to match it or npm installs a second copy alongside.

Can I keep my Jev key out of the project entirely?

Native operations and assertions need no AI key at all. For the natural-language path, point baseURL or JEV_BASE_URL at any compatible System One endpoint, which does not require a Jev API key and never receives the hosted one, so the credential stays wherever your own transport keeps it.

What runtime does it need, and how is it distributed?

Node.js 22.15 or newer. The project is Apache-2.0 while hosted services and model weights are not included, and it is distributed on GitHub Releases rather than a registry, with no postinstall browser download and no global browser daemon required.

How long does a named session last, and where is it stored?

A named session survives separate CLI invocations. Its authenticated loopback endpoint is stored in a private directory, names are scoped to the working directory, and an idle session expires after 30 minutes; commands without --session reuse the existing default session when one exists.

What do CLI and MCP calls return, and how are failures signaled?

All results are JSON, and an error is {ok:false,error:{code,message,retryable:false}}. Exit status is 0 for command success, 1 for errors or assertion failures, and 2 for a stopped or unverified agent or a pending dialog.

CommunityJev Demos & Experiments

Jev Browser — tontoko

Q: Does a green assertion mean the record actually saved?

It means the UI said so. complete/ui-readback is explicitly identified as UI evidence rather than a database durability guarantee, unobserved lists fields not shown after saving, and a model's done opinion alone is never completion. For application-specific acceptance you add expect assertions or an SDK until predicate on top.

Q: Can I keep my Jev key out of the project entirely?

Native operations and assertions need no AI key at all. For the natural-language path, point baseURL or JEV_BASE_URL at any compatible System One endpoint, which does not require a Jev API key and never receives the hosted one, so the credential stays wherever your own transport keeps it.

Q: What runtime does it need, and how is it distributed?

Node.js 22.15 or newer. The project is Apache-2.0 while hosted services and model weights are not included, and it is distributed on GitHub Releases rather than a registry, with no postinstall browser download and no global browser daemon required.

Q: How long does a named session last, and where is it stored?

A named session survives separate CLI invocations. Its authenticated loopback endpoint is stored in a private directory, names are scoped to the working directory, and an idle session expires after 30 minutes; commands without --session reuse the existing default session when one exists.

Q: What do CLI and MCP calls return, and how are failures signaled?

All results are JSON, and an error is {ok:false,error:{code,message,retryable:false}}. Exit status is 0 for command success, 1 for errors or assertion failures, and 2 for a stopped or unverified agent or a pending dialog.

Playwright wrapper that routes natural-language operations and assertions through Jev while clicks, typing and waits stay deterministic, with verification provenance.

See highlights

Open github.com

Stars: 10
Language: JavaScript
License: APACHE-2.0
Published by: Community
Author: tontoko
Last verified: Oct 2026

tontoko/jev-browser

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One grounded Jev/Playwright core: typed SDK, persistent CLI, and MCP server with native browser operations and deterministic assertions.

Forks: 3
Last pushed: Updated Oct 2026

Repo stats from the GitHub API, cached Oct 2026.

This is one of several Jev listings for the same project. The canonical entry is Jev Browser — jkudish.

About this project

Parallel semantic decisions. Deterministic Playwright effects. Explicit verification provenance. Jev Browser combines native Playwright operations with Jev decisions over actual page elements. Use it instead of a Playwright MCP/CLI setup for browser automation, and instead of Stagehand for DOM-grounded act, observe, structured extract, and bounded agent workflows.

Quoted from the project's README. Read the full README.

Tagscommunity jevbest catalog-import awesomejev

Works forJev for Classification Jev for Tool calling

Used inJev for Software & DevTools

Languages: JavaScript

Highlights

Native operations and assertions run with no AI key at all; only the natural-language path touches the model.
Batch frontiers share one retained observation across SDK, CLI and MCP, so later native actions need no extra model call while refs hold.
assertSemantic re-reads its sources before returning, and evidence that changed or vanished is inconclusive rather than a stale pass.
A custom System One endpoint via baseURL or JEV_BASE_URL needs no Jev key and never receives the hosted one.

Watch out

A passing semantic assert is UI evidence, not a database durability guarantee: complete/ui-readback is read that way, unobserved lists fields not shown after saving, and a model's done opinion alone is never treated as completion. A failed or uncertain save is not replayed; an unknown save reconciles read-only first. The package ships as a GitHub Releases tarball rather than a registry install, and it couples tightly to your Playwright version: the peer range is >=1.62.0 <2, an older copy is rejected with a CONFIG error, and Yarn Berry has to add both peers by hand. Copy reviewed against the repository README on 2026-10-04, not from running it.

Questions about this entry

Short answers drawn from the linked project or page.

More Jev resources like this

jev-browse

Browser agent where Jev makes every navigation decision and agent-browser performs clicks and typing, stopping when the named goal page is reached or blocked.