Content
# Jev Browser
**Parallel semantic decisions. Deterministic Playwright effects. Explicit verification provenance.**
Jev Browser combines native Playwright operations with [Jev](https://typesafe.ai) 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.
Native operations and assertions run **without an AI key**. Natural-language operations use the official TypeSafe SDK against hosted Jev by default, or any compatible System One endpoint configured with `baseURL` / `JEV_BASE_URL`. A custom endpoint does not require a Jev API key and never receives the hosted one. The decision backend chooses supplied candidates; it does not generate executable JavaScript or selectors. The project is Apache-2.0 licensed; hosted services and model weights are not included.
[日本語](README.ja.md) · [Migration guide](docs/migration.md) · [API](docs/api.md) · [Semantic verification](docs/semantic-verification.md) · [Security](SECURITY.md) · [Verification](docs/verification.md)
## Install
Node.js **22.15 or newer**. Download the package from [GitHub Releases](https://github.com/tontoko/jev-browser/releases), then install it into your project:
```sh
npm install --save-dev ./tontoko-jev-browser-0.14.2.tgz
npx jev-browser install chromium
```
Or build from source:
```sh
git clone https://github.com/tontoko/jev-browser.git
cd jev-browser
npm ci
npx playwright install chromium
npm run build
node dist/cli.js --help
```
`playwright-core` (`>=1.62.0 <2`) and `zod` (`^4.2.0`) are peer dependencies, so the package shares your project's copies instead of bundling its own. npm 7+ and pnpm install missing peers automatically; with Yarn Berry, add them explicitly: `yarn add -D ./tontoko-jev-browser-<version>.tgz playwright-core zod`. A project on an older `@playwright/test` than the newest release should pin `playwright-core` to the same version (`npm install -D playwright-core@<its version>`); otherwise npm installs the newest `playwright-core` as a second copy. An older `playwright-core` is rejected with a `CONFIG` error.
`jev-browser install` installs the browser build required by the `playwright-core` this package resolves, which is your project's copy. The SDK does not load Playwright Test, so your project's own `@playwright/test` can pass its `page` to `JevBrowser`.
The release tarball includes compiled JavaScript, declarations, the DOM bundle, documentation, and examples. There is no postinstall browser download and no requirement for a global browser daemon. The package is distributed on GitHub Releases; a registry publication is not implied.
## Use existing Playwright Locators, not another selector engine
```ts
import { JevBrowser } from '@tontoko/jev-browser';
import { semanticMatchers } from '@tontoko/jev-browser/playwright';
import { expect as baseExpect } from '@playwright/test';
const browser = new JevBrowser({ page });
const expect = baseExpect.extend(semanticMatchers(browser));
await expect(page.getByTestId('plan')).toSemanticallyMatch(
'Professional annual subscription', { minConfidence: 0.8 },
);
```
`actual: { locator, property: 'text' | 'value' | 'checked' | 'attribute' }` also works directly in `assertSemantic` / `assertSemanticBatch`. Exact values need no model configuration. Ambiguous targets, other Pages and caller-scope escapes are rejected. The optional matcher uses Playwright's existing `expect.extend`; `.not` does not turn uncertain evidence into a pass.
`compareSemantic` compares the observed snapshot. `assertSemantic` also re-reads its actual sources before returning: changed or disappeared evidence is **inconclusive**, not a stale success. It does not repeatedly sample the same evidence until a model agrees. Failures preserve `error.semantic` with expected meanings, all results, both confidence thresholds and current evidence when available; CLI/MCP and named sessions keep that structure.
Independent work shares a frontier across every interface: SDK `locateSemanticBatch` / `compareSemanticBatch` / `assertSemanticBatch`, CLI `semantic_locate_batch` / `semantic_compare_batch` / `semantic_assert_batch`, and matching `browser_…` MCP tools. A target batch returns usable refs from one retained observation; later native actions need no additional model call while those refs remain valid. Source descriptions are sent once per frontier rather than repeated in every question. See [semantic verification](docs/semantic-verification.md) for freshness and exact trust boundaries.
## One request, a complete creation task
```ts
const result = await browser.run(
'Open the new customer form, fill all supplied details, and Save. Do not send a marketing email.',
{ values: {
customer: { name: 'Example Customer', email: 'customer@example.invalid' },
account: { plan: 'Professional annual', region: 'Japan' },
} },
);
```
`run` owns form discovery, parallel field-binding questions, serial native inputs, relevant waits, onward steps and ordinary save confirmations. It checks current input values before a commit, then looks for a new result record and compares its values locally. Long native selects are resolved only when their semantics are needed; exact named values stay local. Standards-associated ARIA comboboxes are handled as bounded open/filter → owned-option → verified-selection interactions. Crowded pages can narrow themselves to a semantic form/result region instead of transmitting a truncated whole page. It does not call the model after every field. Existing native tools and single-action `act` remain available.
Read `result.status`, `verification` and `inputs`: `complete / ui-readback` identifies UI evidence, not a database durability guarantee. `unobserved` explicitly lists fields not shown after saving. A model's done opinion alone is never completion. Add `expect` assertions or an SDK `until` predicate for application-specific acceptance criteria. A failed/uncertain save is not replayed.
Try the self-contained local HTTP example with synthetic records:
```sh
JEV_API_KEY=... npm run example:goal
# Prefer your secret store or Node --env-file over a literal key in shell history.
```
CLI and MCP use the same goal contract; there is no separate agent implementation:
```sh
npx jev-browser run --session work --args - <<'JSON'
{"instruction":"Add a new contact, fill all supplied fields and Save.","values":{"contact":{"name":"Example Contact","email":"contact@example.invalid"}}}
JSON
```
For MCP, send the same JSON to `browser_run`. See [goal execution and boundaries](docs/goal-runtime.md).
### Verified stages and continuation
A single `run()` can save an account, create its membership, then create a reservation. Each observed result becomes a verified checkpoint; the final `expect` runs at the final boundary. Current-field binding and later-stage placement share a parallel decision frontier instead of adding a model round trip for every field or stage assignment.
When stopped work returns `result.continuation.id`, use `browser.resume(id, { values: { missingField: 'value' } })`, CLI `resume ID --session work`, or MCP `browser_resume`. Unknown saves reconcile read-only first and are never automatically replayed. Already verified signatures remain blocked even after scrolling or resuming. Continuation is confined to the same running core, Page, origin and observation scope; values already supplied cannot change. See [checkpoint and continuation semantics](docs/goal-continuation.md).
## CLI: persistent browser, independent commands
```sh
npx jev-browser open https://example.com --session work
npx jev-browser snapshot --session work
# Use the ref returned by snapshot, or a caller-authored Playwright selector:
npx jev-browser click 'a' --session work
npx jev-browser take_screenshot --args '{"filename":"page.png","fullPage":true}' --session work
npx jev-browser close --session work
```
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. `open` defaults to session `default`; commands without `--session` reuse that session when it exists. `--url` without `--session` runs in a fresh browser.
Every command accepts `--args JSON`, and `--args -` reads arguments from stdin. `session` is also available as a JSONL pipe for tools that keep stdin open. All results are JSON. An error is `{"ok":false,"error":{"code":"…","message":"…","retryable":false}}`; see [error codes](docs/api.md#errors-and-automation). Exit status is `0` for command success, `1` for errors/assertion failures, and `2` for a stopped/unverified agent or a pending dialog.
```sh
npx jev-browser open https://example.com --session mobile \
--viewport 390x844 --reduced-motion --color-scheme dark --locale fr-FR
npx jev-browser open https://example.com --session device --options-file device.json
# device.json: {"contextOptions":{"viewport":{"width":390,"height":844},"deviceScaleFactor":3,"isMobile":true,"hasTouch":true,"timezoneId":"Europe/Paris"}}
```
`--viewport WxH`, `--reduced-motion`, `--color-scheme light|dark|no-preference` and `--locale TAG` set Playwright context options. `--options-file FILE` reads JSON with the launch fields of `JevBrowser.launch()` options: `browser`, `headless`, `launchOptions`, `contextOptions`, `storageState`, `userDataDir`, `cdpEndpoint` and `wsEndpoint`. `launchOptions` and `contextOptions` take Playwright's `LaunchOptions` and `BrowserContextOptions`. Explicit flags win over the file (per field inside `contextOptions`), and the file wins over `JEV_BROWSER`. Other keys and invalid values are rejected with the field named. Relative paths resolve against the working directory. These options apply when a browser starts: a one-shot command, `open` of a new session, or the MCP server's first tool call. An existing session keeps the options it was opened with: `open` of a running session with different options fails with `SESSION_MODE_MISMATCH`. A browser attached over CDP keeps its existing context, so context options or a storage state for it fail with `CONFIG`.
```sh
npx jev-browser fill 'input[name=email]' 'user@example.invalid' --session work
npx jev-browser assert --args '{"target":"input[name=email]","property":"value","expected":"user@example.invalid"}' --session work
```
For hosted Jev, set `JEV_API_KEY` or `TYPESAFE_API_KEY`. Those keys are sent only to hosted Jev (`https://api.typesafe.ai`), never to a custom endpoint. For a compatible local/remote System One endpoint, set only `JEV_BASE_URL` (for example `http://127.0.0.1:8765`), plus `JEV_ENDPOINT_API_KEY` (or the SDK `apiKey` option) if that endpoint needs its own key. A key is sent only over HTTPS or to a loopback address; otherwise the AI operation fails with `CONFIG`. Blank key variables count as unset. The endpoint must implement `POST /v1/systemone` with the same `state/questions -> model/answers/usage` envelope:
```sh
npx jev-browser act 'Fill the Name field with "Alice Example"' --session work
npx jev-browser act 'Fill the email field with email' \
--values '{"email":"user@example.invalid"}' --session work
npx jev-browser extract 'Read the invoice total' \
--fields '{"total":{"type":"number","description":"Total, not subtotal"}}' --session work
```
Explicit `values` are kept out of decision payloads. Quoted values are copied verbatim from the caller's instruction, which itself is sent to Jev. Page text and page-echoed input can contain private data: see [the data boundary](SECURITY.md).
## MCP: native and natural-language tools
For a reviewer that should discover the product from visible UI, use a separate `--screen-only` session. It exposes viewport images and coordinate mouse, focused keyboard, scroll and history inputs through one shared `screen` command. DOM/ARIA snapshots, selectors, semantic operations, network diagnostics and URL metadata are unavailable through that session's command surface. Every action returns current images and actual timestamps; an outer vision-capable model supplies the review judgment. Add `--screen-follow-popups` (SDK `screenFollowPopups`) to observe a new tab the page opens instead of closing it. See [screen-only review](docs/screen-review.md) for trusted setup, recordings, freshness and remaining browser limitations. When the caller or decision model is text-only, the opt-in `screen_decide` command (MCP `browser_screen_decide`, SDK `screenDecide`) captures the viewport once, has an image-capable OpenAI-compatible Chat Completions endpoint that you configure with `--vision-base-url` and `--vision-model` describe it, and answers your questions with Jev from that description; screenshots leave the machine only then and only to that endpoint. See [image understanding](docs/image-understanding.md). Agent hosts connect through the existing SDK, CLI or MCP surface; this package has no harness-specific adapter. See [migration](docs/migration.md#removing-the-pi-adapter-0100) for the removed `./pi` entry point.
After installing the tarball, configure your MCP client:
```json
{
"mcpServers": {
"jev-browser": {
"command": "node",
"args": ["/absolute/project/node_modules/@tontoko/jev-browser/dist/mcp-stdio.js"],
"env": { "JEV_API_KEY": "YOUR_KEY" }
}
}
}
```
The environment entry is unnecessary for native operations. Prefer your client's secret store over putting real keys into committed JSON. Browser launch is lazy: tool discovery does not start a browser. The server accepts the CLI launch flags, for example `"args": [".../mcp-stdio.js", "--viewport", "390x844", "--options-file", "/absolute/path/device.json"]`. If a launch fails or the browser disconnects, the next tool call starts a new browser; no call is retried automatically. In `--screen-only` mode a failed startup or a lost browser is final, as `browser_close` is.
Cookie/storage, routing, tracing and page-evaluation tools are opt-in: add `--caps storage,network,trace,evaluate` (any subset) to the server arguments. Tools that are not enabled are not listed. `browser_file_upload` reads only from directories given with `--file-root DIR`; without one, uploads fail with `FILE_ACCESS_DENIED`.
Tool calls to one server run one at a time in arrival order, so parallel calls wait instead of returning `BUSY`. A waiting call ends when the client cancels it, and an explicit `timeoutMs` argument includes the wait. `browser_close` is not queued, so it can stop a long-running call. Read-only tools do not change the page, but `browser_snapshot`, `browser_observe`, `browser_extract` and `browser_semantic_locate` replace this session's short-lived refs and any pending `browser_observe` plan.
`browser_snapshot` provides refs for `browser_click`, `browser_type`, and other native tools. `browser_act`, `browser_observe`, `browser_extract`, and `browser_run` use the **same core** as the SDK. Native `browser_assert` verifies facts without asking a model. Tools also cover tabs, frames, dialogs, uploads/downloads, screenshots, PDF, mouse/keyboard, console messages, request metadata and, with `--caps`, storage, cookies, routing and traces. Console messages, request metadata and downloads are reported for the selected tab unless `allTabs` is set; each entry carries a `pageId` that matches `browser_tabs`, and a download keeps a stable `id` for saving or cancelling it.
Tool input schemas describe each argument. Rules that JSON Schema cannot express without top-level `oneOf`/`anyOf`, such as exactly one of `instruction` or `planId` for `browser_act`, are stated in the argument descriptions and still enforced by the shared command schemas. Integer arguments accept at most 2147483647.
## SDK: existing Playwright Page and assertions
```ts
import { test, expect } from '@playwright/test';
import { JevBrowser } from '@tontoko/jev-browser';
import { z } from 'zod';
test('save a name', async ({ page }) => {
await page.setContent(`
<label>Name<input></label>
<button onclick="document.querySelector('h1').textContent='Saved'">Save</button>
<h1>Pending</h1>
`);
const browser = new JevBrowser({ page });
try {
await browser.act('Fill the Name field with name', { values: { name: 'Alice' } });
await browser.act('Click Save');
await expect(page.getByRole('heading')).toHaveText('Saved');
const result = await browser.extract('Read the heading', z.object({ title: z.string() }));
expect(result.data.title).toBe('Saved');
expect(result.evidence.title.text).toBe('Saved');
} finally {
await browser.close(); // does not close the borrowed Page/context/browser
}
});
```
`JevBrowser.launch()` owns its resources. Chromium, Firefox, WebKit, persistent profiles, CDP, and Playwright WebSocket connections are supported. The SDK exposes `browser.page`, so native Playwright assertions, locators, fixtures and application-specific verification remain available.
A borrowed Page keeps Playwright's default dialog handling outside Jev operations. Jev holds an `alert`, `confirm` or `prompt` only while one of its own operations runs, and returns it as a pending `dialog` for `handle_dialog`. Your own `page.click()` on a button that opens `confirm()` is dismissed by Playwright as usual and does not block later Jev operations. File choosers follow the same rule. Pass `captureDialogs: true` to also hold dialogs and file choosers that open between operations; `JevBrowser.launch()`, the CLI and the MCP server do this by default.
### Semantic locate and confidence-aware assertions
Use deterministic Playwright/native assertions whenever exact browser truth is available. When the UI expresses the same meaning with different wording, semantic verification is explicit rather than silently mixed into deterministic assertions:
```ts
const target = await browser.locateSemantic('The control that manages the current subscription');
await browser.native({ command: 'click', ref: target.ref });
const result = await browser.compareSemantic({
actual: { description: 'Current subscription plan' },
expected: 'Professional annual subscription',
minConfidence: 0.8,
});
await browser.assertSemantic({
actual: { description: 'Billing state' },
expected: 'Paid',
minConfidence: 0.9,
});
```
Semantic comparison returns grounded evidence, `passed | failed | inconclusive`, the comparison `confidence`, the separate `sourceConfidence`, and both thresholds. `minConfidence` defaults to `0.8`. `minSourceConfidence` defaults to the effective `minConfidence`, but can be tuned separately when source-selection scores have a different distribution. **Confidence is a Jev decision score, not a probability that the assertion is correct.** Low-confidence and insufficient-evidence outcomes never pass. A below-threshold source stops there instead of spending a second comparison request. Exact grounded equality likewise short-circuits locally without a second semantic comparison call.
Independent assertions can use `compareSemanticBatch()`: source discovery is one decision frontier and unresolved comparisons another, so more independent fields increase questions before they increase serial decision depth. Results expose `serialDecisionDepth`, provider/token usage, `providerMs`, `observationMs`, and local `verificationMs`. See [Semantic verification](docs/semantic-verification.md).
CLI commands `semantic_locate`, `semantic_compare`, and `semantic_assert` and MCP tools `browser_semantic_locate`, `browser_semantic_compare`, and `browser_semantic_assert` use the same SDK core.
### Structured extraction, grounded by record
```ts
const result = await browser.extract(
'Read open invoices, preserving table order',
z.object({ invoices: z.array(z.object({ number: z.string(), total: z.number() })) }),
{ recordsScope: 'tbody tr' },
);
// result.data.invoices, result.evidence['invoices.0.total']
```
Nested objects and arrays are supported. Every array item comes from an observed row/card, and its fields are selected only from that record's text. `recordsScope` selects the records; otherwise semantic rows, list items and articles are used. Values and hrefs retain source evidence. Text longer than 700 characters is observed as its first 700 characters with `truncated: true` and is never copied. Missing required values fail instead of being invented. Unsafe integers should be extracted as strings. Schema defaults, catch fallbacks, generated summaries, and value-changing transforms are not extraction operations.
### Bounded agent, deterministic completion
```ts
const result = await browser.agent({
maxSteps: 8,
until: async page => page.getByText('Saved', { exact: true }).isVisible(),
}).execute({
instruction: 'Enter name in the Name field and save',
values: { name: 'Alice' },
});
expect(result.status).toBe('complete');
```
`agent().execute()` delegates to `run()`. An SDK `until` returning literal `true`, or a supplied `expect` assertion, produces caller-verified completion once requested inputs are covered. When both are supplied, both must pass. It should promptly return `false` while work remains. Without caller checks, a fresh matching result record can produce `complete / ui-readback` with explicit evidence coverage. Model-only completion stays `unverified`. Prompt/ambiguous dialogs, missing inputs and budgets stop explicitly. Mutation failures are never automatically retried; see `error.partial` before deciding what to do next.
## Scope and migration
This is a **functional alternative**, not a binary-compatible re-export of Microsoft or Browserbase packages. Tool configuration, CLI flags, SDK types, and result envelopes have documented differences. [The migration guide](docs/migration.md) maps the supported workflows and remaining boundaries.
The AI layer is DOM/ARIA-based. Native HTML controls, very long select lists, open shadow roots, child frames, and standards-associated ARIA comboboxes are covered by the shared core. Native screenshots and coordinate mouse operations are available to an outer vision-capable client, but Jev does not infer Canvas coordinates or invent text from images. Arbitrary widget conventions without a grounded ownership/value signal, cloud session infrastructure, browser extensions, generated summaries, and arbitrary Node-side MCP code execution are not part of this package. Explicit page evaluation is off by default; trusted SDK callers already have the full Playwright Page.
## Verify and contribute
```sh
npm run check
npm run check:examples
npm run check:package
# Explicit real-provider tests, synthetic pages only:
npm run test:live
npm run test:live:semantic
```
Default tests use real browsers, deterministic injected choices, and local HTTP fixtures. Live tests are opt-in and never run against production accounts. See [CONTRIBUTING.md](CONTRIBUTING.md) and [the verification record](docs/verification.md).
## Supplied values with different option wording
For native selects, `run(..., {values:{country:"Japan"}, semanticInputs:{"/country":0.8}})` permits Jev to map that value to an observed option such as `日本` / `JP`. The JSON Pointer is both an explicit disclosure grant and a confidence policy. Ordinary named values remain local; there is no synonym dictionary. Unresolved supplied values return `unresolved-input` with grounded blockers rather than pretending the caller supplied nothing. See [progress and input resolution](docs/observed-input-resolution.md).
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