# getScorer()

The `getScorer()` method retrieves a specific scorer that was registered with the Mastra instance using its registration key. This method provides type-safe access to scorers and throws an error if the requested scorer isn't found.

## Usage example

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

// Get a specific scorer by key
const relevancyScorer = mastra.getScorer('relevancyScorer')

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

**key** (`string`): The registration key of the scorer to retrieve. This should match a key used when registering scorers in the Mastra constructor.

## Returns

**scorer** (`MastraScorer`): The MastraScorer instance associated with the provided key.

## Error handling

This method throws a `MastraError` if:

- The scorer with the specified key isn't found
- No scorers are registered with the Mastra instance

```typescript
try {
  const scorer = mastra.getScorer('nonExistentScorer')
} catch (error) {
  if (error.id === 'MASTRA_GET_SCORER_NOT_FOUND') {
    console.log('Scorer not found, using default evaluation')
  }
}
```

## Related

- [listScorers()](https://mastra.ai/reference/core/listScorers) - Get all registered scorers
- [getScorerById()](https://mastra.ai/reference/core/getScorerById) - Get a scorer by its id property
- [Custom Scorers](https://mastra.ai/docs/evals/custom-scorers) - Learn how to create custom scorers