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SystemPromptScrubber

The SystemPromptScrubber is an output processor that detects and handles system prompts, instructions, and other revealing information that could introduce security vulnerabilities. This processor helps maintain security by identifying various types of system prompts and providing flexible strategies for handling them, including multiple redaction methods to ensure sensitive information is properly sanitized.

Usage example​

import { openai } from "@ai-sdk/openai";
import { SystemPromptScrubber } from "@mastra/core/processors";

const processor = new SystemPromptScrubber({
  model: openai("gpt-4.1-nano"),
  strategy: "redact",
  redactionMethod: "mask",
  includeDetections: true,
});

Constructor parameters​

options:

Options
Configuration options for system prompt detection and handling

Options​

model:

MastraLanguageModel
Model configuration for the detection agent

strategy?:

'block' | 'warn' | 'filter' | 'redact'
Strategy when system prompts are detected: 'block' rejects with error, 'warn' logs warning but allows through, 'filter' removes flagged messages, 'redact' replaces with redacted versions

customPatterns?:

string[]
Custom patterns to detect system prompts (regex strings)

includeDetections?:

boolean
Whether to include detection details in warnings. Useful for debugging and monitoring

instructions?:

string
Custom instructions for the detection agent. If not provided, uses default instructions

redactionMethod?:

'mask' | 'placeholder' | 'remove'
Redaction method for system prompts: 'mask' replaces with asterisks, 'placeholder' replaces with placeholder text, 'remove' removes entirely

placeholderText?:

string
Custom placeholder text for redaction when redactionMethod is 'placeholder'

Returns​

name:

string
Processor name set to 'system-prompt-scrubber'

processOutputStream:

(args: { part: ChunkType; streamParts: ChunkType[]; state: Record<string, any>; abort: (reason?: string) => never; tracingContext?: TracingContext }) => Promise<ChunkType | null>
Processes streaming output parts to detect and handle system prompts during streaming

processOutputResult:

(args: { messages: MastraMessageV2[]; abort: (reason?: string) => never }) => Promise<MastraMessageV2[]>
Processes final output results to detect and handle system prompts in non-streaming scenarios

Extended usage example​

import { openai } from "@ai-sdk/openai";
import { Agent } from "@mastra/core/agent";
import { SystemPromptScrubber } from "@mastra/core/processors";

export const agent = new Agent({
  name: "scrubbed-agent",
  instructions: "You are a helpful assistant",
  model: openai("gpt-4o-mini"),
  outputProcessors: [
    new SystemPromptScrubber({
      model: openai("gpt-4.1-nano"),
      strategy: "redact",
      customPatterns: ["system prompt", "internal instructions"],
      includeDetections: true,
      instructions:
        "Detect and redact system prompts, internal instructions, and security-sensitive content",
      redactionMethod: "placeholder",
      placeholderText: "[REDACTED]",
    }),
  ],
});