# Vanilla / headless

> The core engine with no framework at all.

`@wcgw/vibe-check-core` is plain TypeScript with zero runtime dependencies. Wire
the engine up by hand, read snapshots however you like, and clean up when you're
done.

## Install

```bash
pnpm add @wcgw/vibe-check-core
```

## The full lifecycle

```ts
import { VibeCheckEngine } from '@wcgw/vibe-check-core'

const engine = new VibeCheckEngine()
engine.start()

// Read the current snapshot at any time:
const snapshot = engine.getSnapshot()
console.info(snapshot.frameRate.fps, snapshot.domNodeCount)

// Or subscribe to every tick (~every 500ms):
const unsubscribe = engine.onSnapshot((snap) => {
  console.info(snap.frameRate.fps, snap.issues.length)
})

// Always clean up:
unsubscribe()
engine.stop()
```

`getSnapshot()` returns the current `VibeSnapshot` — frame rate, long frames, web
vitals, memory, resources, console counts, `domNodeCount`, and the current
`issues` array. `onSnapshot` returns an unsubscribe function; `stop()` tears down
every collector and detector and restores any patched globals.

## Beacon-only mode

To feed your AI agent without rendering anything, give the engine a `beaconUrl`.
It POSTs snapshots to `<beaconUrl>/api/snapshot` on its own interval — you don't
subscribe or render at all:

```ts
import { VibeCheckEngine } from '@wcgw/vibe-check-core'

const engine = new VibeCheckEngine({
  beaconUrl: 'http://127.0.0.1:4200',
  projectId: 'my-project',
  beaconIntervalMs: 2000, // default
})
engine.start()

// Stop when the page/session ends:
window.addEventListener('pagehide', () => engine.stop())
```

## Feature detection is automatic

The engine feature-detects browser APIs — `PerformanceObserver`, LoAF, layout
shift, `performance.memory` — and simply skips collectors the host doesn't
support. Missing metrics read as empty (or `null` for memory) rather than
throwing. You can query support directly if you need to branch on it:

```ts
import {
  hasLongAnimationFrame,
  hasPerformanceMemory,
} from '@wcgw/vibe-check-core'

if (!hasPerformanceMemory()) {
  // Non-Chromium: the memory-leak detector will stay quiet.
}
```

See the [Core API reference](/docs/reference/core-api) for every export.