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# Workflow\.classifier()

The `.classifier()` method adds a configured [`Classifier`](https://mastra.ai/reference/classifier/classifier) as a declarative workflow step. It returns a JSON-safe `{ answers, usage }` object that can be consumed by later steps and existing control-flow methods such as [`.branch()`](https://mastra.ai/reference/workflows/workflow-methods/branch).

## Usage example

```typescript
const workflow = createWorkflow({
  id: 'ticket-triage',
  inputSchema: z.object({ message: z.string() }),
  outputSchema: z.any(),
})
  .map({ message: { initData: true, path: 'message' } })
  .classifier(router)
  .branch([
    [async ({ inputData }) => inputData.answers.route.choice === 'billing', billingStep],
    [async ({ inputData }) => inputData.answers.route.choice === 'support', supportStep],
    [async () => true, fallbackStep],
  ])
  .commit()
```

When a classifier instance is passed, question keys and choice literals are inferred in downstream steps. The classifier must contain constructor-configured questions.

## Parameters

**classifierOrId** (`Classifier<QUESTIONS> | string`): A configured classifier instance, or the ID of a classifier registered on the Mastra instance. String references are resolved at execution time.

**options** (`ClassifierStepOptions`): Classifier and step options, including model-call maxRetries, providerOptions, workflow retries, metadata, and an optional id.

**stepOptions** (`{ id?: string }`): The step's call-site ID within the workflow. Defaults to the classifier ID. This value takes precedence over options.id.

## Returns

**workflow** (`Workflow`): The workflow instance for method chaining

## Input mapping

The classifier evaluates the complete previous step output. Insert [`.map()`](https://mastra.ai/reference/workflows/workflow-methods/map) before `.classifier()` to select or reshape its input.

```typescript
workflow
  .map({
    message: { initData: true, path: 'message' },
    locale: { initData: true, path: 'locale' },
  })
  .classifier(router)
```

Mappings use the same validated path grammar as other workflow steps and persist in serialized workflow graphs.

## Output

- Choice answers expose `answers.<question>.choice` and may include `probabilities`.
- Score answers expose `answers.<question>.score` and may include `probabilities`.
- Boolean answers expose the raw `P(true)` value as `answers.<question>.probability`. Apply an explicit threshold when routing.
- `usage` contains normalized token usage.

## Retries and errors

`maxRetries` controls retries of the classifier's model call. `retries` controls retries of the workflow step. The workflow abort signal is forwarded to the classifier. Classifier errors fail the step. `.classifier()` doesn't apply fail-open behavior.

## Referencing a classifier by ID

Register the classifier on the same `Mastra` instance that runs the workflow:

```typescript
export const mastra = new Mastra({
  classifiers: { router },
  workflows: { workflow },
})
```

For a typed string reference, supply the configured question type explicitly:

```typescript
workflow.classifier<typeof router.questions>('router')
```

## Related

- [Classifier](https://mastra.ai/reference/classifier/classifier)
- [Step class](https://mastra.ai/reference/workflows/step)
- [Workflow.branch()](https://mastra.ai/reference/workflows/workflow-methods/branch)
- [Dynamic workflow definition](https://mastra.ai/reference/workflows/dynamic-workflow-definition)