heal-playwright-tracer

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heal-playwright-tracer

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Open-source statement-level Playwright tracer, purpose-built for AI agents. Analyzes test runs with increased accuracy.

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<h1 align="center">
  <a href="https://heal.dev/">
    <img width="240" src="assets/heal-logo.svg" alt="heal">
  </a>
</h1>
<p align="center">
  <p align="center">Open-source statement-level Playwright tracer, purpose-built for AI agents.</p>
</p>

<h4 align="center">
  <a href="https://app.heal.dev/">SaaS</a> |
  <a href="https://heal.dev/">Website</a> |
  <a href="https://docs.heal.dev/">Docs</a>
</h4>

# @heal-dev/heal-playwright-tracer

heal-playwright-tracer is an agent-first diagnostic layer for your Playwright tests. It gives agents
(and humans) everything they need to quickly analyze test results.

👉 **Add this to your playwright config, run your tests, point Claude to the improved heal trace, get more accurate test diagnosis**

## Why

The playwright trace doesn't contain enough data for LLM-based agents such as Claude or Open Code to analyze tests results reliably.
That's because the trace ifs focused on locator evaluation, while real-life tests also evaluate non-playwright code.
Heal adds the missing instrumentation layer to let LLM agents work their magic.
And it's useful for humans in complex test codebases, too!

| Feature        | Playwright Trace      | Heal Tracer          | Example: What Heal Adds                                                                   |
| -------------- | --------------------- | -------------------- | ----------------------------------------------------------------------------------------- |
| Granularity    | Action-level          | Statement-level      | Shows `let x = calculate()` line-by-line, not just the final `page.click()`.              |
| Data Format    | ZIP/Binary            | NDJSON Stream        | `{"type":"step","file":"auth.spec.ts","line":12,"val":{"user":"dev"}}`                    |
| Visual Context | Standard screenshots  | Highlighted locators | An image where the target button is outlined in a neon overlay to prove hit-box accuracy. |
| Variable State | Limited/Debugger only | Full Variable Values | Captures that `status_code` was `403` inside a hidden helper function.                    |
| Error Detail   | Standard stack trace  | Serialized Errors    | A JSON object containing the DOM snapshot at the exact millisecond of the throw.          |
| Timing         | Action durations      | Per-statement timing | Identifies that a specific `if` statement logic took `2.5s` to evaluate.                  |
| Correlations   | Loose logs/network    | API Correlations     | Links `Trace_ID_99` directly to `Source_Line_45` in the NDJSON stream.                    |

## Install

```sh
npm install -D @heal-dev/heal-playwright-tracer
```

Wire the Babel plugin **and** the reporter in `playwright.config.ts`:

```ts
// playwright.config.ts
import { defineConfig } from '@playwright/test';

export default defineConfig({
  // @ts-ignore — `babelPlugins` is a supported Playwright option not yet in its public types
  '@playwright/test': {
    babelPlugins: [
      [
        require.resolve('@heal-dev/heal-playwright-tracer/code-hook-injector'),
        { include: [/\/tests\//] },
      ],
    ],
  },
  reporter: [['@heal-dev/heal-playwright-tracer/reporter']],
});
```

Both are required: if you wire the Babel plugin without the
reporter, the fixture fails fast on the first test of every worker.
For _why_ the reporter is mandatory (crash rescue, Playwright
attachment copy, execution-history index), see
[`docs/configuration.md`](docs/configuration.md#reporter).

If you prefer to keep the config fully typed, declare the
`babelPlugins` option once at the top of the file instead of using
`@ts-ignore`:

```ts
declare module '@playwright/test' {
  interface Config {
    '@playwright/test'?: {
      babelPlugins?: Array<[string, object?]>;
    };
  }
}
```

Per-test output lands at
`heal-traces/<executionId>/<playwrightTestId>/<attempt>/heal-traces.ndjson`.
See [Output layout](#output-layout) below for the full tree.

## Output layout

Every run produces a self-contained execution dir under:
`heal-traces/<executionId>/<playwrightTestId>/<attempt>/heal-traces.ndjson`.

```
<cwd>/heal-traces/
├── executions.ndjson                                   # append-only run index
└── <executionId>/                                      # auto-generated uuidv4 per run
    ├── execution.json                                  # per-run manifest
    └── <playwrightTestId>/                             # Playwright testInfo.testId
        └── <attempt>/                                  # 1-indexed
            ├── heal-traces.ndjson
            ├── trace.zip                               # if Playwright recorded one
            ├── screenshots/
            │   └── stmt-0001.png
            └── videos/
                └── video.webm
```

Keys are shaped `{executionId}/{testId}/{attempt}/...` so the layout
maps cleanly onto any object-store key prefix if you ship traces
elsewhere later.

History is **append-only** — runs accumulate, nothing is pruned.
Clean up manually with `rm -rf heal-traces/<id>/` when needed.

> **Note:** add `heal-traces/` to your `.gitignore` — these are local
> build artefacts and should never be committed.

`<executionId>` is a uuidv4 the reporter generates at the start of
each run; the trace viewer uses it to scope and group artefacts per
run.

## Usage

1. After installing Heal, run your tests with the usual `npx playwright test` command.
2. You should see `heal-traces.ndjson`.
3. You can ask Claude or another agent to use those to understand your test results.

### Viewing traces

A small CLI ships alongside the tracer so humans can browse the
captured traces in a local browser without setting up a Heal account:

```sh
npx heal-tracer view
```

The CLI starts a local HTTP server on a free OS-assigned port,
reads `<cwd>/heal-traces/`, lists every recorded execution in the
header dropdown (newest first), and opens the latest one in your
default browser. Switch executions from the dropdown to inspect
history. Press Ctrl+C to stop.

#### Options

| Flag            | Description                                                                                                                                                   |
| --------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `--port <port>` | Bind a fixed port instead of an OS-assigned ephemeral one. Useful when an external frontend needs a stable URL. Falls back to the `HEAL_TRACER_PORT` env var. |
| `--api-only`    | Serve only the `/api/*` routes — no SPA bundle, no browser auto-open. For driving the REST API from a separate frontend dev server.                           |
| `--verbose`     | Mirror spawned subprocess output (`heal analyze`, `heal login`) to the tracer console.                                                                        |

To consume the REST API from your own frontend during development,
run the server on a fixed port without the bundled UI:

```sh
npx heal-tracer view --api-only --port 3001
# or, via env (e.g. from a .env loaded with `node --env-file`, direnv, or your shell):
HEAL_TRACER_PORT=3001 npx heal-tracer view --api-only
```

CORS is wide-open (`Access-Control-Allow-Origin: *`), so a frontend
on its own dev server can `fetch('http://localhost:3001/api/executions')`
cross-origin with no extra setup. The API is unauthenticated and
`localhost`-bound by design — don't expose it on a public interface.

### Claude Skill

See [this Claude skill](docs/SKILL.md) for a starter.

## Sample output

`heal-data/heal-traces.ndjson` — one record per line:

```ndjson
{"kind":"test-header","schemaVersion":1,"test":{"title":"it works","file":"tests/example.spec.ts","context":{"testId":"...","attempt":1}}}
{"kind":"statement","statement":{"loc":{"line":5},"source":"await page.goto('https://example.com')","durationMs":412,"status":"ok","children":[...]}}
{"kind":"statement","statement":{"loc":{"line":6},"source":"await expect(page.getByRole('heading')).toBeVisible()","durationMs":73,"status":"ok"}}
{"kind":"test-result","status":"passed","duration":1234,"stdout":"...","stderr":""}
```

Schema: [`src/domain/trace-event-recorder/model/statement-trace-schema.ts`](src/domain/trace-event-recorder/model/statement-trace-schema.ts)
(also exported as `@heal-dev/heal-playwright-tracer/statement-trace-schema`).

### Screenshots

Every statement that calls a patched Playwright **locator action**
(`click`, `fill`, `hover`, `press`, …) or a **locator assertion**
(`expect(locator).toBeVisible()`, `toHaveText()`, …) produces a
PNG screenshot with the targeted element outlined via an overlay
drawn in-page — so the agent sees _what Playwright was actually
pointing at_ at the moment the action ran, not just the raw page.

Files are written to the per-test `heal-data/` directory and
referenced on the corresponding statement via the `screenshot`
field:

```ndjson
{"kind":"statement","statement":{"source":"await page.getByRole('button', { name: 'Submit' }).click()","status":"ok","screenshot":"stmt-0007.png"}}
{"kind":"statement","statement":{"source":"await expect(page.getByRole('alert')).toBeVisible()","status":"ok","screenshot":"stmt-0008.png"}}
```

Statements that don't touch a locator (plain JS, utility calls,
`page.goto`) have no `screenshot` field — capture is scoped to the
Playwright surface where it adds diagnostic signal.

## Architecture, and extending the tracer

See [development.md](docs/development.md)

## Caveats

The Babel plugin rewrites every leaf statement with a `try/catch/finally`
and three hook calls — the same shape of transformation Istanbul applies
for code coverage. Two consequences to be aware of:

- **Instrumented files are larger.** Each statement gains a wrapper, so
  on-disk size of transformed test files grows noticeably (typically
  ~2–4×, depending on statement density). This affects the files
  Playwright loads into workers, not your application bundle.
- **Tests run slightly slower.** The per-statement hook overhead is
  small in absolute terms but not free — expect a modest slowdown on
  CPU-bound test code. I/O-bound tests (the common case: `await
page.click(...)`, network, navigation) are dominated by the browser
  and barely move.

Scope the `include` filter in `playwright.config.ts` so only your
`tests/` directory is instrumented — never your app code or
`node_modules` — to keep the cost contained.

## License

This project is licensed under the **GNU Affero General Public License v3.0 (AGPL-3.0)**, except for the `tracer-viewer-bundle` which is a vendored, free to use version of the Heal trace viewer.
See the [LICENSE](LICENSE) file for the full text.

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