@mastra/evals

@mastra/evals

A comprehensive evaluation framework for assessing AI model outputs across multiple dimensions.

Installation

npm install @mastra/evals

Overview

@mastra/evals provides a suite of evaluation metrics for assessing AI model outputs. The package includes both LLM-based and NLP-based metrics, enabling both automated and model-assisted evaluation of AI responses.

Features

LLM-Based Metrics

• Answer Relevancy

  • Evaluates how well an answer addresses the input question
  • Considers uncertainty weighting for more nuanced scoring
  • Returns detailed reasoning for scores

• Bias Detection

  • Identifies potential biases in model outputs
  • Analyzes opinions and statements for bias indicators
  • Provides explanations for detected biases
  • Configurable scoring scale

• Context Precision & Relevancy

  • Assesses how well responses use provided context
  • Evaluates accuracy of context usage
  • Measures relevance of context to the response
  • Analyzes context positioning in responses

• Faithfulness

  • Verifies that responses are faithful to provided context
  • Detects hallucinations or fabricated information
  • Evaluates claims against provided context
  • Provides detailed analysis of faithfulness breaches

• Prompt Alignment

  • Measures how well responses follow given instructions
  • Evaluates adherence to multiple instruction criteria
  • Provides per-instruction scoring
  • Supports custom instruction sets

• Toxicity

  • Detects toxic or harmful content in responses
  • Provides detailed reasoning for toxicity verdicts
  • Configurable scoring thresholds
  • Considers both input and output context

NLP-Based Metrics

• Completeness

  • Analyzes structural completeness of responses
  • Identifies missing elements from input requirements
  • Provides detailed element coverage analysis
  • Tracks input-output element ratios

• Content Similarity

  • Measures text similarity between inputs and outputs
  • Configurable for case and whitespace sensitivity
  • Returns normalized similarity scores
  • Uses string comparison algorithms for accuracy

• Keyword Coverage

  • Tracks presence of key terms from input in output
  • Provides detailed keyword matching statistics
  • Calculates coverage ratios
  • Useful for ensuring comprehensive responses

Usage

Basic Example

import { ContentSimilarityMetric, ToxicityMetric } from '@mastra/evals';

// Initialize metrics
const similarityMetric = new ContentSimilarityMetric({
  ignoreCase: true,
  ignoreWhitespace: true,
});

const toxicityMetric = new ToxicityMetric({
  model: openai('gpt-4'),
  scale: 1, // Optional: adjust scoring scale
});

// Evaluate outputs
const input = 'What is the capital of France?';
const output = 'Paris is the capital of France.';

const similarityResult = await similarityMetric.measure(input, output);
const toxicityResult = await toxicityMetric.measure(input, output);

console.log('Similarity Score:', similarityResult.score);
console.log('Toxicity Score:', toxicityResult.score);

Context-Aware Evaluation

import { FaithfulnessMetric } from '@mastra/evals';

// Initialize with context
const faithfulnessMetric = new FaithfulnessMetric({
  model: openai('gpt-4'),
  context: ['Paris is the capital of France', 'Paris has a population of 2.2 million'],
  scale: 1,
});

// Evaluate response against context
const result = await faithfulnessMetric.measure(
  'Tell me about Paris',
  'Paris is the capital of France with 2.2 million residents',
);

console.log('Faithfulness Score:', result.score);
console.log('Reasoning:', result.reason);

Metric Results

Each metric returns a standardized result object containing:

• score: Normalized score (typically 0-1)
• info: Detailed information about the evaluation
• Additional metric-specific data (e.g., matched keywords, missing elements)

Some metrics also provide:

• reason: Detailed explanation of the score
• verdicts: Individual judgments that contributed to the final score

Telemetry and Logging

The package includes built-in telemetry and logging capabilities:

• Automatic evaluation tracking through Mastra Storage
• Integration with OpenTelemetry for performance monitoring
• Detailed evaluation traces for debugging

import { attachListeners } from '@mastra/evals';

// Enable basic evaluation tracking
await attachListeners();

// Store evals in Mastra Storage (if storage is enabled)
await attachListeners(mastra);
// Note: When using in-memory storage, evaluations are isolated to the test process.
// When using file storage, evaluations are persisted and can be queried later.

Environment Variables

Required for LLM-based metrics:

• OPENAI_API_KEY: For OpenAI model access
• Additional provider keys as needed (Cohere, Anthropic, etc.)

Package Exports

// Main package exports
import { evaluate } from '@mastra/evals';
// NLP-specific metrics
import { ContentSimilarityMetric } from '@mastra/evals/nlp';

Related Packages

• @mastra/core: Core framework functionality
• @mastra/engine: LLM execution engine
• @mastra/mcp: Model Context Protocol integration