LLM Guard

What It Does

LLM Guard intercepts all hexr_llm() calls and scans prompts and responses for security threats using multiple detection strategies.

Scanning Pipeline

Prompt Injection Detection

Incoming prompt is analyzed for injection attacks, jailbreak attempts, and adversarial patterns.

PII Scanner

Detects and optionally redacts personally identifiable information (names, emails, SSNs, etc.).

Secrets Scanner

Catches API keys, tokens, passwords, and other credentials before they reach the LLM.

Token Limit Check

Validates the prompt fits within the configured token budget for the model.

LLM Provider

The sanitized prompt is forwarded to the configured LLM provider.

Response Scanner

The LLM response is scanned for leaked secrets, hallucinated PII, and policy violations.

Topic Boundary Check

Ensures the response stays within the agent’s configured topic boundaries.

Prompt → Injection Check → PII Scan → Secrets Scan → Token Check → LLM → Response Scan → Topic Check → Agent

Scanners

Scanner	Direction	What It Catches
Prompt Injection	Input	Jailbreak attempts, system prompt extraction, role-play attacks
PII Detection	Input + Output	Email addresses, phone numbers, SSNs, credit cards
Secrets Detection	Input + Output	API keys, passwords, tokens, private keys
Token Limit	Input	Prevents context window overflow attacks
Topic Boundary	Output	Detects off-topic responses that may indicate manipulation

OWASP Top 10 for GenAI Coverage

OWASP Risk	LLM Guard Protection
LLM01: Prompt Injection	Prompt injection scanner
LLM02: Insecure Output	Response content scanner
LLM06: Sensitive Information	PII + secrets scanner
LLM07: Insecure Plugin Design	Gateway credential scoping
LLM09: Overreliance	Topic boundary check

Integration

LLM Guard is automatically invoked by hexr_llm() — no code changes required:

# LLM Guard scans this prompt before it reaches OpenAI
response = hexr_llm(
    provider="openai",
    model="gpt-4o",
    prompt="Analyze this customer data: ...",
)
# LLM Guard scans the response before returning

To manually scan:

from hexr.guard import scan_prompt, scan_output

result = scan_prompt("user input here")
if result.flagged:
    print(f"Blocked: {result.scanner} - {result.reason}")

Configuration

Environment Variable	Default	Description
`ENABLED_SCANNERS`	`all`	Comma-separated list of active scanners
`PII_DETECTION_THRESHOLD`	`0.85`	Confidence threshold for PII detection
`INJECTION_DETECTION_MODEL`	`built-in`	Prompt injection detection model
`BLOCK_ON_DETECTION`	`true`	Block or warn on detection

Observability

LLM Guard is fully instrumented with OpenTelemetry. Every scan generates span attributes on the parent hexr.llm.call span and emits dedicated metrics.

Span Attributes

When LLM Guard blocks a prompt or response, the following attributes are set on the hexr.llm.call span:

Attribute	Type	Description
`hexr.guard.prompt_blocked`	`bool`	`true` if the input prompt was blocked
`hexr.guard.scanners`	`string`	Scanner results that triggered the prompt block
`hexr.guard.output_blocked`	`bool`	`true` if the LLM response was blocked
`hexr.guard.output_scanners`	`string`	Scanner results that triggered the output block

Blocked requests set the span status to ERROR with a description like "Blocked by LLM Guard" or "Output blocked by LLM Guard".

Metrics

Metric	Type	Description
`hexr_guard_scans_total`	Counter	Total scans by direction (`input`/`output`) and scanner
`hexr_guard_blocks_total`	Counter	Total blocks by direction and scanner
`hexr_guard_scan_duration_seconds`	Histogram	Scan latency by direction

Grafana Dashboard

The Security dashboard includes an LLM Guard panel showing:

Block rate over time (prompt vs. response)
Top triggered scanners
Scan latency percentiles
Blocks by tenant and agent

See Observability Stack for the full telemetry pipeline.

Platform Overview

Pod Containers

Cluster Services

Infrastructure

What It Does

Scanning Pipeline

Scanners

OWASP Top 10 for GenAI Coverage

Integration

Configuration

Observability

Span Attributes

Metrics

Grafana Dashboard

​What It Does

​Scanning Pipeline

​Scanners

​OWASP Top 10 for GenAI Coverage

​Integration

​Configuration

​Observability

​Span Attributes

​Metrics

​Grafana Dashboard

What It Does

Scanning Pipeline

Scanners

OWASP Top 10 for GenAI Coverage

Integration

Configuration

Observability

Span Attributes

Metrics

Grafana Dashboard