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What is a Guard?

A guard is a protection module focused on a specific threat category. While a guardrail defines your overall protection policy, guards do the actual work of detecting and handling threats. Think of guards like specialized security personnel. One guard watches for weapons. Another checks IDs. Another monitors for suspicious behavior. Each has a specific job; together they provide comprehensive protection. Dome guards work the same way—one detects prompt injection, another catches PII, another flags toxic content. Guards contain one or more detectors (the detection logic) and define what action to take when threats are found. You configure guards based on what threats matter for your use case.

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Guard Categories

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Security Guards

Security guards protect against adversarial attacks on your agent:
GuardProtects Against
Prompt InjectionInstructions embedded in user input designed to hijack agent behavior
JailbreakSocial engineering attempts to bypass safety guidelines
Encoding AttackObfuscated malicious content (base64, unicode, etc.)
Security guards are essential for any agent exposed to untrusted input—which is most agents in production.

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Privacy Guards

Privacy guards protect sensitive information:
GuardProtects Against
PII DetectionPersonal identifiable information (names, emails, SSNs, etc.)
Secrets DetectionAPI keys, passwords, credentials in input or output
Data LeakageSensitive business data escaping through agent responses
Privacy guards can detect, redact, or block. Redaction is common—replace the SSN with [REDACTED] rather than blocking the entire request.

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Moderation Guards

Moderation guards enforce content standards:
GuardProtects Against
ToxicityHate speech, harassment, threats, severe profanity
Sexual ContentExplicit or inappropriate sexual material
ViolenceGraphic violence, self-harm content
MisinformationDemonstrably false claims on high-stakes topics
Moderation guards are configurable by sensitivity. A customer service bot needs strict moderation; an adult content platform has different requirements.

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Integrity Guards

Integrity guards maintain agent behavior boundaries:
GuardProtects Against
Topic RestrictionResponses outside the agent’s intended domain
Persona ViolationBreaks from the agent’s defined character or role
Instruction OverrideAttempts to change the agent’s system prompt behavior
Integrity guards help agents stay in their lane—answering questions they should answer, refusing questions they shouldn’t.

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Guard Configuration

Each guard has configurable parameters: 
{
    "prompt-injection": {
        "type": "security",
        "methods": ["prompt-injection-deberta", "heuristic-rules"],
        "action": "block",
        "threshold": 0.8
    }
}
ParameterDescription
typeGuard category (security, privacy, moderation, integrity)
methodsWhich detectors to use within this guard
actionWhat to do on detection: log, warn, redact, block
thresholdConfidence threshold for triggering action (0.0-1.0)

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Multiple Detectors per Guard

Guards can use multiple detectors for defense in depth. A prompt injection guard might combine:
  • Fast heuristics: Pattern matching for known injection signatures
  • ML classifier: DeBERTa model trained on injection examples
  • LLM judge: Secondary model evaluating whether input looks like an attack
Multiple detectors catch more attacks but add latency. Configure based on your security/performance tradeoff.

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Input vs. Output Guards

Guards run on both input and output, but different guards matter for each:
DirectionPriority Guards
InputPrompt injection, jailbreak, PII (to protect your systems)
OutputToxicity, PII (to protect users), topic restriction, data leakage
Some guards run on both. PII detection on input prevents sensitive data from reaching your agent; PII detection on output prevents your agent from exposing data in responses.

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Guard Results

When a guard runs, it produces: 
{
    "guard": "prompt-injection",
    "triggered": true,
    "confidence": 0.94,
    "action_taken": "block",
    "detector_results": [
        {"method": "deberta", "score": 0.94, "triggered": true},
        {"method": "heuristics", "score": 0.0, "triggered": false}
    ],
    "evidence": "Detected instruction override pattern: 'ignore previous...'"
}
Results include which detectors fired, their confidence scores, and evidence explaining the detection. This transparency helps you tune guards and investigate incidents.

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Next Steps

Guardrail

How guards compose into pipelines

Detector

The detection engines inside guards

Configure Guardrails

Set up guards for your agent

Available Guards

Reference of all guard types