ModerationProcessor

The ModerationProcessor is a hybrid processor that can be used for both input and output processing to provide content moderation using an LLM to detect inappropriate content across multiple categories. This processor helps maintain content safety by evaluating messages against configurable moderation categories with flexible strategies for handling flagged content.

Usage example

import { ModerationProcessor } from '@mastra/core/processors'

const processor = new ModerationProcessor({
  model: 'openrouter/openai/gpt-oss-safeguard-20b',
  threshold: 0.7,
  strategy: 'block',
  categories: ['hate', 'harassment', 'violence'],
})

Constructor parameters

<PropertiesTable content={[ { name: 'options', type: 'Options', description: 'Configuration options for content moderation', isOptional: false, properties: [ { type: 'Options', parameters: [ { name: 'model', type: 'MastraModelConfig', description: 'Model configuration for the moderation agent', isOptional: false, }, { name: 'categories', type: 'string[]', description: 'Categories to check for moderation. If not specified, uses default OpenAI categories', isOptional: true, default: "['hate', 'hate/threatening', 'harassment', 'harassment/threatening', 'self-harm', 'self-harm/intent', 'self-harm/instructions', 'sexual', 'sexual/minors', 'violence', 'violence/graphic']", }, { name: 'threshold', type: 'number', description: 'Confidence threshold for flagging (0-1). Content is flagged if any category score exceeds this threshold', isOptional: true, default: '0.5', }, { name: 'strategy', type: "'block' | 'warn' | 'filter'", description: "Strategy when content is flagged: 'block' rejects with error, 'warn' logs warning but allows through, 'filter' removes flagged messages", isOptional: true, default: "'block'", }, { name: 'instructions', type: 'string', description: 'Custom moderation instructions for the agent. If not provided, uses default instructions based on categories', isOptional: true, default: 'undefined', }, { name: 'includeScores', type: 'boolean', description: 'Whether to include confidence scores in logs. Useful for tuning thresholds and debugging', isOptional: true, default: 'false', }, { name: 'chunkWindow', type: 'number', description: 'Number of previous chunks to include for context when moderating stream chunks. If set to 1, includes the previous part, etc.', isOptional: true, default: '0 (no context window)', }, { name: 'providerOptions', type: 'ProviderOptions', description: "Provider-specific options passed to the internal moderation agent. Use this to control model behavior like reasoning effort for thinking models (e.g., { openai: { reasoningEffort: 'low' } })", isOptional: true, default: 'undefined', }, ], }, ], }, ]} />

Returns

<PropertiesTable content={[ { name: 'id', type: 'string', description: "Processor identifier set to 'moderation'", isOptional: false, }, { name: 'name', type: 'string', description: 'Optional processor display name', isOptional: true, }, { name: 'processInput', type: '(args: { messages: MastraDBMessage[]; abort: (reason?: string) => never; tracingContext?: TracingContext }) => Promise<MastraDBMessage[]>', description: 'Processes input messages to moderate content before sending to LLM', isOptional: false, }, { name: 'processOutputStream', type: '(args: { part: ChunkType; streamParts: ChunkType[]; state: Record<string, any>; abort: (reason?: string) => never; tracingContext?: TracingContext }) => Promise<ChunkType | null | undefined>', description: 'Processes streaming output parts to moderate content during streaming', isOptional: false, }, ]} />

Extended usage example

Input processing

import { Agent } from '@mastra/core/agent'
import { ModerationProcessor } from '@mastra/core/processors'

export const agent = new Agent({
  name: 'moderated-agent',
  instructions: 'You are a helpful assistant',
  model: 'openai/gpt-5.4',
  inputProcessors: [
    new ModerationProcessor({
      model: 'openrouter/openai/gpt-oss-safeguard-20b',
      categories: ['hate', 'harassment', 'violence'],
      threshold: 0.7,
      strategy: 'block',
      instructions: 'Detect and flag inappropriate content in user messages',
      includeScores: true,
    }),
  ],
})

Output processing with batching

When using ModerationProcessor as an output processor, it's recommended to combine it with BatchPartsProcessor to optimize performance. The BatchPartsProcessor batches stream chunks together before passing them to the moderator, reducing the number of LLM calls required for moderation.

import { Agent } from '@mastra/core/agent'
import { BatchPartsProcessor, ModerationProcessor } from '@mastra/core/processors'

export const agent = new Agent({
  name: 'output-moderated-agent',
  instructions: 'You are a helpful assistant',
  model: 'openai/gpt-5.4',
  outputProcessors: [
    // Batch stream parts first to reduce LLM calls
    new BatchPartsProcessor({
      batchSize: 10,
    }),
    // Then apply moderation on batched content
    new ModerationProcessor({
      model: 'openrouter/openai/gpt-oss-safeguard-20b',
      strategy: 'filter',
      chunkWindow: 1,
    }),
  ],
})

Related

• Guardrails