# getScorerById()

The `getScorerById()` method retrieves a scorer by searching for its `id` property (or `name` property as a fallback) rather than the registration key. This is useful when you know the scorer's id but not necessarily how it was registered in the Mastra instance.

## Usage example

```typescript
import { mastra } from './mastra'

// Get a scorer by its id property
const relevancyScorer = mastra.getScorerById('answer-relevancy-scorer')

const weatherAgent = mastra.getAgent('weatherAgent')

// Use the scorer to evaluate an AI output
await weatherAgent.generate('What is the weather in Rome', {
  scorers: {
    answerRelevancy: {
      scorer: relevancyScorer,
    },
  },
})
```

## Parameters

**id** (`string`): The id property of the scorer to retrieve. This should match the 'id' field specified when creating the scorer with createScorer(). The method will also search by 'name' property as a fallback.

## Returns

**scorer** (`MastraScorer`): The MastraScorer instance that has the matching id (or name) property.

## Error handling

This method throws a `MastraError` if:

- No scorer with the specified id is found
- No scorers are registered with the Mastra instance

```typescript
try {
  const scorer = mastra.getScorerById('non-existent-scorer')
} catch (error) {
  if (error.id === 'MASTRA_GET_SCORER_BY_ID_NOT_FOUND') {
    console.log('Scorer with that id not found')
  }
}
```

## Related

- [getScorer()](https://mastra.ai/reference/core/getScorer) - Get a scorer by its registration key
- [listScorers()](https://mastra.ai/reference/core/listScorers) - Get all registered scorers
- [createScorer()](https://mastra.ai/reference/evals/create-scorer) - Learn how to create scorers with ids