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# filterRun()

Creates a `prepareRun` function from declarative options. Pass the result to `createScorer()` to filter messages and limit context size. It also drops unnecessary fields before the scorer pipeline runs.

Use [`filterRun()`](#usage-example) for declarative filtering. Write a custom `prepareRun` function directly when you need imperative logic that `filterRun()` doesn't cover. See [Custom scorers: input filtering](https://mastra.ai/docs/evals/custom-scorers) for more.

## Usage example

The following example creates a scorer that only sees tool invocations and text messages, limited to the 20 most recent context messages:

```typescript
import { createScorer, filterRun } from '@mastra/core/evals'

const toolScorer = createScorer({
  id: 'tool-usage',
  description: 'Evaluates tool usage patterns',
  type: 'agent',
  prepareRun: filterRun({
    partTypes: ['tool-invocation', 'text'],
    maxRememberedMessages: 20,
  }),
}).generateScore(({ run }) => {
  // run.input.rememberedMessages contains only tool and text messages
  // run.output contains only tool and text messages
  return 1
})
```

### Filter by tool name

Keep only messages involving specific tools:

```typescript
import { createScorer, filterRun } from '@mastra/core/evals'

const fileEditScorer = createScorer({
  id: 'file-edit-quality',
  description: 'Evaluates file editing patterns',
  type: 'agent',
  prepareRun: filterRun({
    toolNames: ['write_file', 'string_replace_lsp', 'view'],
  }),
}).generateScore(({ run }) => {
  // Only messages with these tool calls remain
  return 1
})
```

### Drop fields

Remove fields the scorer doesn't need:

```typescript
import { createScorer, filterRun } from '@mastra/core/evals'

const simpleScorer = createScorer({
  id: 'response-length',
  description: 'Checks response length',
  type: 'agent',
  prepareRun: filterRun({
    dropRequestContext: true,
    dropExpectedTrajectory: true,
    dropGroundTruth: true,
    maxOutputMessages: 5,
  }),
}).generateScore(({ run }) => {
  return run.output.length > 0 ? 1 : 0
})
```

## Parameters

**options** (`FilterRunOptions`): Configuration object that controls what data the scorer receives.

**options.partTypes** (`MastraPartType[]`): Keep only messages whose parts match these types. Each entry is prefix-matched against the message part's type. Plain text messages (no tool invocations) are always kept unless explicitly excluded. System messages and tagged system messages are never filtered.

**options.toolNames** (`string[]`): Keep only tool-invocation messages for these specific tools. Each entry is prefix-matched against the tool name. Non-tool messages (text, data) are unaffected.

**options.maxRememberedMessages** (`number`): Maximum number of messages to keep in remembered messages (context). Takes from the end (most recent). Applied after type and tool filtering.

**options.maxOutputMessages** (`number`): Maximum number of messages to keep in the output. Takes from the end. Applied after type and tool filtering.

**options.dropRequestContext** (`boolean`): Remove request context from the run entirely.

**options.dropExpectedTrajectory** (`boolean`): Remove expected trajectory from the run.

**options.dropGroundTruth** (`boolean`): Remove ground truth from the run.

**Returns:** `(run: ScorerRun) => ScorerRun`. A function suitable for the `prepareRun` option on [`createScorer()`](https://mastra.ai/reference/evals/create-scorer).

## Part types

The `partTypes` option accepts `MastraPartType` values. Each value is prefix-matched, so `'data-'` matches all data part types.

| Type                | Description                                  |
| ------------------- | -------------------------------------------- |
| `'text'`            | Text content parts                           |
| `'tool-invocation'` | Tool call and result parts                   |
| `'reasoning'`       | Chain-of-thought reasoning parts             |
| `'step-start'`      | Step marker parts                            |
| `'image'`           | Image parts                                  |
| `'file'`            | File parts                                   |
| `'source'`          | Source reference parts                       |
| `'source-document'` | Source document parts                        |
| `'data-'`           | All data parts (matches any `data-*` prefix) |
| `'data-om-'`        | Observational memory data parts              |
| `'data-workspace-'` | Workspace data parts                         |
| `'data-sandbox-'`   | Sandbox data parts                           |
| `'data-tool-'`      | Tool-related data parts                      |

## Filtering behavior

- **Part type filtering** applies to both `input.rememberedMessages` and `output` when they contain agent message arrays.
- **Tool name filtering** only affects messages that contain tool invocations. Text-only messages pass through.
- **System messages** (`systemMessages`, `taggedSystemMessages`) are never filtered, regardless of `partTypes` or `toolNames`.
- **Message limits** (`maxRememberedMessages`, `maxOutputMessages`) apply after type and tool filtering, taking the most recent messages.
- When both `partTypes` and `toolNames` are set, a message must satisfy both filters to be kept.