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# Classifier

`Classifier` asks a decision model one or more fixed-domain questions about shared state. Use it when your application needs a typed choice, numeric score, or boolean probability without parsing generated text.

A classifier only returns evaluation results. Your application decides how to use them, for example by selecting a route or comparing a probability with a safety threshold.

`Classifier` requires a decision model (`DecisionModelV4`, or the deprecated `EvaluationModelV4`, optionally wrapped in `MastraDecisionModel`). It doesn't accept a `'provider/model'` string, a bare model ID, or a language model.

## Basic usage

This example uses the [TypeSafe AI provider](https://ai-sdk.dev/providers/ai-sdk-providers/typesafe-ai). Make sure to set the `TYPESAFE_AI_API_KEY` environment variable. To use another provider, see [Decision models](#decision-models).

Install the provider package:

**npm**:

```bash
npm install @ai-sdk/typesafe-ai
```

**pnpm**:

```bash
pnpm add @ai-sdk/typesafe-ai
```

**Yarn**:

```bash
yarn add @ai-sdk/typesafe-ai
```

**Bun**:

```bash
bun add @ai-sdk/typesafe-ai
```

Define questions in the constructor when every evaluation uses the same question set. Keep the question object literal so TypeScript can infer the answer keys and choice values.

```typescript
import { Classifier } from '@mastra/core/classifier'
import { typeSafeAi } from '@ai-sdk/typesafe-ai'

const classifier = new Classifier({
  id: 'request-classifier',
  model: typeSafeAi.decisionModel('jev-latest'),
  questions: {
    route: {
      type: 'choice',
      instructions: 'Choose the team that should handle this request.',
      criteria: {
        billing: 'Questions about invoices, charges, or refunds',
        support: 'Questions about using or troubleshooting the product',
      },
    },
    urgent: {
      type: 'boolean',
      instructions: 'Does this request require an immediate response?',
    },
  },
})

const result = await classifier.decide({
  state: {
    subject: 'Duplicate charge',
    message: 'I was charged twice for the same subscription.',
  },
})

result.answers.route.choice // 'billing' | 'support'
result.answers.urgent.probability // P(true), from 0 to 1
```

The decision model receives every question with the same `state`. When a question omits `instructions`, its question name is used instead.

## Decision models

The examples on this page follow the [TypeSafe AI provider setup](https://ai-sdk.dev/providers/ai-sdk-providers/typesafe-ai#setup) in the AI SDK documentation. Other AI SDK providers, including OpenAI, Anthropic, and Google, also expose a `decisionModel()` factory (previously `evaluationModel()`, still available as a deprecated alias). Mastra calls `doDecide()` and falls back to `doEvaluate()` for older providers. See [provider models](https://ai-sdk.dev/docs/ai-sdk-core/decisions#provider-models) for the full list, supported model IDs, and how each provider answers questions.

Each provider exports a ready-made instance, which is what the examples on this page use. See [AI SDK providers](https://ai-sdk.dev/providers/ai-sdk-providers) for the others.

Pass a key explicitly by calling the factory instead:

```typescript
import { createTypeSafeAi } from '@ai-sdk/typesafe-ai'

const model = createTypeSafeAi({ apiKey: process.env.TYPESAFE_AI_API_KEY }).decisionModel(
  'jev-latest',
)
```

## Constructor

```typescript
new Classifier(options)
```

**id** (`string`): A non-empty identifier used in tracing and error context.

**model** (`DecisionModelV4 | EvaluationModelV4 | MastraDecisionModel`): An AI SDK decision model or a Mastra decision model wrapper. The model declares which question types it supports.

**questions** (`ClassifierQuestions`): A non-empty record of named questions. Omit this field to supply the questions to each decide() call instead.

Constructor questions and per-call questions are mutually exclusive. If the constructor includes `questions`, `decide()` rejects a `questions` option at compile time. If the constructor omits them, every `decide()` call must provide them. A processor, workflow step, or scorer classifies through a configured classifier, which requires constructor questions.

## Question types

Question names become keys in `result.answers`. Each question supports an optional `instructions` field containing a JSON-compatible value. Criteria values can also contain JSON-compatible data, not only strings.

### Choice questions

A choice question selects one key from a non-empty `criteria` record.

```typescript
const questions = {
  sentiment: {
    type: 'choice',
    instructions: 'Classify the customer sentiment.',
    criteria: {
      positive: 'The customer is satisfied or complimentary.',
      neutral: 'The customer has no clear positive or negative sentiment.',
      negative: 'The customer is dissatisfied or frustrated.',
    },
  },
} as const
```

The answer contains the selected `choice`. When the provider includes `probabilities`, the record must contain every choice key and sum to `1` within the provider's declared rounding precision.

```typescript
const answer = {
  type: 'choice',
  choice: 'negative',
  probabilities: {
    positive: 0.05,
    neutral: 0.15,
    negative: 0.8,
  },
}
```

### Score questions

A score question uses an ordered array with at least two levels. Array indexes define the score range. For three criteria, valid scores range from `0` through `2`, including fractional values.

```typescript
const questions = {
  quality: {
    type: 'score',
    instructions: 'Score the response quality.',
    criteria: ['Incorrect or unhelpful', 'Partially correct', 'Correct and complete'],
  },
} as const
```

A provider can return a fractional score and an optional probability for each level:

```typescript
const answer = {
  type: 'score',
  score: 1.7,
  probabilities: {
    '0': 0.05,
    '1': 0.2,
    '2': 0.75,
  },
}
```

### Boolean questions

A boolean question returns the estimated probability that the answer is `true`. The value is always between `0` and `1`. It isn't the confidence of whichever outcome is more likely.

```typescript
const questions = {
  unsafe: {
    type: 'boolean',
    instructions: 'Does the message contain unsafe content?',
    criteria: {
      true: 'The message contains unsafe content.',
      false: 'The message is safe.',
    },
  },
} as const
```

The `criteria` field is optional for boolean questions. When present, its `true` and `false` descriptions are also optional.

```typescript
const answer = {
  type: 'boolean',
  probability: 0.92,
}
```

## Designing questions

These rules keep a question answerable from the state:

- Ask for one judgment. A question that moves when either of two fields changes can't be routed on.
- Keep criteria exclusive. `strong: 'A good fit'` and `partial: 'Maybe a fit'` leak probability between them.
- Give a score enough levels to represent intermediate values.
- Add an escape level when the list isn't closed. Three teams and no `other` forces every input into a team.
- Put fields in `state`, not in `instructions`. One changed field then moves one answer.

To check a question, change one field of the state and confirm one answer moves.

## `decide(options)`

Answers all questions against the supplied state.

`evaluate(options)` is a deprecated alias for `decide(options)` and will be removed in a future release.

**state** (`ClassifierState`): The JSON-compatible state evaluated by every question.

**questions** (`ClassifierQuestions`): The questions to evaluate. Required when the constructor omitted questions.

**abortSignal** (`AbortSignal`): Cancels the active provider request and any wait between retry attempts.

**providerOptions** (`SharedV4ProviderOptions`): Provider-specific options forwarded unchanged to the decision model.

**maxRetries** (`number`): The number of retries allowed after retryable provider API errors. Must be a non-negative integer. (Default: `2`)

### Per-call questions

Omit `questions` from the constructor when the question set changes between evaluations. The answer type is inferred from the questions supplied to that call.

```typescript
import { Classifier } from '@mastra/core/classifier'
import { typeSafeAi } from '@ai-sdk/typesafe-ai'

const classifier = new Classifier({
  id: 'dynamic-classifier',
  model: typeSafeAi.decisionModel('jev-latest'),
})

const result = await classifier.decide({
  state: { response: 'Your refund has been processed.' },
  questions: {
    tone: {
      type: 'choice',
      criteria: {
        empathetic: 'Acknowledges the customer and responds with care',
        neutral: 'States the outcome without emotional language',
      },
    },
  },
})

result.answers.tone.choice // 'empathetic' | 'neutral'
```

## Return value

`decide()` returns `Promise<ClassifierResult<QUESTIONS>>`.

**answers** (`ClassifierAnswers<QUESTIONS>`): One typed answer for each configured question.

**usage** (`ClassifierUsage`): Token usage reported by the provider. totalTokens is the sum of inputTokens and outputTokens, with missing values counted as zero.

**warnings** (`SharedV4Warning[]`): Warnings returned by the decision model.

**rounding** (`{ probabilityDecimals?: number; scoreDecimals?: number }`): The precision the provider used for probabilities and scores.

**providerMetadata** (`SharedV4ProviderMetadata`): Provider-specific metadata returned by the decision model.

**response** (`ClassifierResult["response"]`): Provider response metadata. Mastra supplies the current time and configured model ID when the provider omits them.

```typescript
interface ClassifierUsage {
  inputTokens?: number
  outputTokens?: number
  totalTokens: number
}

interface ClassifierResponse {
  id?: string
  timestamp: Date
  modelId: string
  headers?: Record<string, string | undefined>
  body?: unknown
}
```

## Validation and errors

`Classifier` validates inputs before provider input/output and validates provider output before returning it.

Input validation includes:

- `id` must be a non-empty string.
- `state`, instructions, and criteria must be JSON-compatible.
- The question record and choice criteria must not be empty.
- Score criteria must contain at least two defined levels.
- Every question type must be supported by the decision model.
- `maxRetries` must be a non-negative integer.

Provider responses must contain exactly one matching answer for each question. The classifier also rejects invalid choices, out-of-range scores or probabilities, incomplete probability distributions, non-finite token counts, malformed warnings, and invalid response timestamps.

Only retryable AI SDK `APICallError` failures are retried. Other errors reject immediately. When all retries fail, `decide()` rethrows the last provider error. Aborting the supplied signal rejects with the signal's abort reason, including when cancellation occurs during retry backoff.

## Observability

When an active Mastra span exists, `decide()` creates a `CLASSIFIER_EVALUATION` child span. It records the classifier and model identifiers, provider, question count and types, attempts, duration, and token usage.

The span doesn't include the evaluated state, question instructions, criteria, answers, probabilities, provider response body, or generated text.

## Customize provider responses

`Classifier` automatically wraps a raw AI SDK decision model in `MastraDecisionModel`. Pass your own wrapper when provider output needs normalization before validation.

```typescript
import { Classifier, MastraDecisionModel, type DecisionModelResult } from '@mastra/core/classifier'
import { typeSafeAi } from '@ai-sdk/typesafe-ai'

class NormalizedDecisionModel extends MastraDecisionModel {
  protected override transformResult(result: DecisionModelResult): DecisionModelResult {
    return {
      ...result,
      answers: normalizeAnswers(result.answers),
    }
  }
}

const classifier = new Classifier({
  id: 'normalized-classifier',
  model: new NormalizedDecisionModel(
    typeSafeAi.decisionModel('jev-latest'),
  ),
})
```

`transformResult()` runs after the provider call and before `Classifier` validates the response.

`MastraEvaluationModel` and `EvaluationModelResult` are deprecated aliases for `MastraDecisionModel` and `DecisionModelResult` and will be removed in a future release.

## Registering classifiers

Register classifiers on the `Mastra` instance to share them across your application and retrieve them by key or ID. When a registered classifier is evaluated without an active trace, it starts a root `CLASSIFIER_EVALUATION` span through the `Mastra` instance's configured observability provider.

```typescript
import { Mastra } from '@mastra/core'
import { Classifier } from '@mastra/core/classifier'
import { typeSafeAi } from '@ai-sdk/typesafe-ai'

export const safety = new Classifier({
  id: 'safety',
  model: typeSafeAi.decisionModel('jev-latest'),
  questions: {
    unsafe: { type: 'boolean' },
  },
})

export const mastra = new Mastra({
  classifiers: { safety },
})

mastra.getClassifier('safety')
mastra.getClassifierById('safety')
mastra.listClassifiers()
```

## Using classifiers in workflows

A classifier with constructor-configured questions can be added to a workflow with [`createStep(classifier)`](https://mastra.ai/reference/workflows/step) or [`.classifier()`](https://mastra.ai/reference/workflows/workflow-methods/classifier). Workflow output contains complete typed `answers` and normalized `usage`.

```typescript
import { safety } from '../index'

const workflow = createWorkflow({
  id: 'ticket-triage',
  inputSchema: z.object({ message: z.string() }),
  outputSchema: z.any(),
})
  .map({ message: { initData: true, path: 'message' } })
  .classifier<typeof safety.questions>('safety')
  .commit()
```

A string reference resolves through the `Mastra` instance at execution time. The ID doesn't carry the question types, so supply them with a type argument to keep the answers typed. In Studio, the workflow graph shows the step as a classifier node.

The workflow adapter doesn't include warnings, raw provider responses, headers, or provider metadata in step output. Use direct `decide()` calls or classifier observability when you need that provider-level detail.

## Related

- [ClassifierProcessor](https://mastra.ai/reference/processors/classifier-processor)
- [ModelSelectionProcessor](https://mastra.ai/reference/processors/model-selection-processor)
- [createClassifierScorer()](https://mastra.ai/reference/evals/create-classifier-scorer)
- [Workflow.classifier()](https://mastra.ai/reference/workflows/workflow-methods/classifier)
- [Step class](https://mastra.ai/reference/workflows/step)
- [getClassifier()](https://mastra.ai/reference/core/getClassifier)
- [getClassifierById()](https://mastra.ai/reference/core/getClassifierById)
- [listClassifiers()](https://mastra.ai/reference/core/listClassifiers)