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Factual Consistency Scanner

This scanner is designed to assess if the given content contradicts or refutes a certain statement or prompt. It acts as a tool for ensuring the consistency and correctness of language model outputs, especially in contexts where logical contradictions can be problematic.

Attack scenario

When interacting with users or processing information, it's important for a language model to not provide outputs that directly contradict the given inputs or established facts. Such contradictions can lead to confusion or misinformation. The scanner aims to highlight such inconsistencies in the output.

How it works

The scanner leverages pretrained natural language inference (NLI) models from HuggingFace, such as MoritzLaurer/deberta-v3-base-zeroshot-v1.1-all-33 ( same model that is used for the BanTopics scanner), to determine the relationship between a given prompt and the generated output.

Natural language inference is the task of determining whether a “hypothesis” is true (entailment), false ( contradiction), or undetermined (neutral) given a “premise”.

This calculated score is then compared to a configured threshold. Outputs that cross this threshold are flagged as contradictory.


from llm_guard.output_scanners import FactualConsistency

scanner = FactualConsistency(minimum_score=0.7)
sanitized_output, is_valid, risk_score = scanner.scan(prompt, model_output)

Optimization Strategies

Read more


Test setup:

  • Platform: Amazon Linux 2
  • Python Version: 3.11.6
  • Input length: 140
  • Test times: 5

Run the following script:

python benchmarks/ output FactualConsistency


Instance Latency Variance Latency 90 Percentile Latency 95 Percentile Latency 99 Percentile Average Latency (ms) QPS
AWS m5.xlarge 3.01 234.94 262.31 284.20 180.00 777.78
AWS m5.xlarge with ONNX 0.09 98.62 103.28 107.01 89.00 1573.02
AWS g5.xlarge GPU 34.23 295.96 388.34 462.24 110.70 1264.69
AWS g5.xlarge GPU with ONNX 0.01 11.18 13.02 14.49 7.42 18879.18
Azure Standard_D4as_v4 4.14 271.39 302.78 327.89 205.62 680.87
Azure Standard_D4as_v4 with ONNX 0.01 62.73 63.71 64.51 59.82 2340.44