# 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 is not 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 is not 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