Agent Evaluation

Testing and benchmarking LLM agents including behavioral testing, capability assessment, reliability metrics, and production monitoring—where even top agents achieve less than 50% on real-world benchmarks

Capabilities

• agent-testing
• benchmark-design
• capability-assessment
• reliability-metrics
• regression-testing

Prerequisites

• Knowledge: Testing methodologies, Statistical analysis basics, LLM behavior patterns
• Skills_recommended: autonomous-agents, multi-agent-orchestration
• Required skills: testing-fundamentals, llm-fundamentals

Scope

• Does_not_cover: Model training evaluation (loss, perplexity), Fairness and bias testing, User experience testing
• Boundaries: Focus is agent capability and reliability, Covers functional and behavioral testing

Ecosystem

Primary_tools

• AgentBench - Multi-environment benchmark for LLM agents (ICLR 2024)
• τ-bench (Tau-bench) - Sierra's real-world agent benchmark
• ToolEmu - Risky behavior detection for agent tool use
• Langsmith - LLM tracing and evaluation platform

Alternatives

• Braintrust - When: Need production monitoring integration LLM evaluation and monitoring
• PromptFoo - When: Focus on prompt-level evaluation Prompt testing framework

Deprecated

• Manual testing only

Patterns

Statistical Test Evaluation

Run tests multiple times and analyze result distributions

When to use: Evaluating stochastic agent behavior

interface TestResult { testId: string; runId: string; passed: boolean; score: number; // 0-1 for partial credit latencyMs: number; tokensUsed: number; output: string; expectedBehaviors: string[]; actualBehaviors: string[]; }

interface StatisticalAnalysis { passRate: number; confidence95: [number, number]; meanScore: number; stdDevScore: number; meanLatency: number; p95Latency: number; behaviorConsistency: number; }

class StatisticalEvaluator { private readonly minRuns = 10; private readonly confidenceLevel = 0.95;

async evaluateAgent(
    agent: Agent,
    testSuite: TestCase[]
): Promise<EvaluationReport> {
    const results: TestResult[] = [];

    // Run each test multiple times
    for (const test of testSuite) {
        for (let run = 0; run < this.minRuns; run++) {
            const result = await this.runTest(agent, test, run);
            results.push(result);
        }
    }

    // Analyze by test
    const byTest = this.groupByTest(results);
    const testAnalyses = new Map<string, StatisticalAnalysis>();

    for (const [testId, testResults] of byTest) {
        testAnalyses.set(testId, this.analyzeResults(testResults));
    }

    // Overall analysis
    const overall = this.analyzeResults(results);

    return {
        overall,
        byTest: testAnalyses,
        concerns: this.identifyConcerns(testAnalyses),
        recommendations: this.generateRecommendations(testAnalyses)
    };
}

private analyzeResults(results: TestResult[]): StatisticalAnalysis {
    const passes = results.filter(r => r.passed);
    const passRate = passes.length / results.length;

    // Calculate confidence interval for pass rate
    const z = 1.96;  // 95% confidence
    const se = Math.sqrt((passRate * (1 - passRate)) / results.length);
    const confidence95: [number, number] = [
        Math.max(0, passRate - z * se),
        Math.min(1, passRate + z * se)
    ];

    const scores = results.map(r => r.score);
    const latencies = results.map(r => r.latencyMs);

    return {
        passRate,
        confidence95,
        meanScore: this.mean(scores),
        stdDevScore: this.stdDev(scores),
        meanLatency: this.mean(latencies),
        p95Latency: this.percentile(latencies, 95),
        behaviorConsistency: this.calculateConsistency(results)
    };
}

private calculateConsistency(results: TestResult[]): number {
    // How consistent are the behaviors across runs?
    if (results.length < 2) return 1;

    const behaviorSets = results.map(r => new Set(r.actualBehaviors));
    let consistencySum = 0;
    let comparisons = 0;

    for (let i = 0; i < behaviorSets.length; i++) {
        for (let j = i + 1; j < behaviorSets.length; j++) {
            const intersection = new Set(
                [...behaviorSets[i]].filter(x => behaviorSets[j].has(x))
            );
            const union = new Set([...behaviorSets[i], ...behaviorSets[j]]);
            consistencySum += intersection.size / union.size;
            comparisons++;
        }
    }

    return consistencySum / comparisons;
}

private identifyConcerns(analyses: Map<string, StatisticalAnalysis>): Concern[] {
    const concerns: Concern[] = [];

    for (const [testId, analysis] of analyses) {
        if (analysis.passRate < 0.8) {
            concerns.push({
                testId,
                type: 'low_pass_rate',
                severity: analysis.passRate < 0.5 ? 'critical' : 'high',
                message: `Pass rate ${(analysis.passRate * 100).toFixed(1)}% below threshold`
            });
        }

        if (analysis.behaviorConsistency < 0.7) {
            concerns.push({
                testId,
                type: 'inconsistent_behavior',
                severity: 'high',
                message: `Behavior consistency ${(analysis.behaviorConsistency * 100).toFixed(1)}% indicates unstable agent`
            });
        }

        if (analysis.stdDevScore > 0.3) {
            concerns.push({
                testId,
                type: 'high_variance',
                severity: 'medium',
                message: 'High score variance suggests unpredictable quality'
            });
        }
    }

    return concerns;
}

}

Behavioral Contract Testing

Define and test agent behavioral invariants

When to use: Need to ensure agent stays within bounds

// Define behavioral contracts: what agent must/must not do

interface BehavioralContract { name: string; description: string; mustBehaviors: BehaviorAssertion[]; mustNotBehaviors: BehaviorAssertion[]; contextual?: ConditionalBehavior[]; }

interface BehaviorAssertion { behavior: string; detector: (output: AgentOutput) => boolean; severity: 'critical' | 'high' | 'medium' | 'low'; }

class BehavioralContractTester { private contracts: BehavioralContract[] = [];

// Example contract for a customer service agent
defineCustomerServiceContract(): BehavioralContract {
    return {
        name: 'customer_service_agent',
        description: 'Contract for customer service agent behavior',

        mustBehaviors: [
            {
                behavior: 'responds_politely',
                detector: (output) =>
                    !this.containsRudeLanguage(output.text),
                severity: 'critical'
            },
            {
                behavior: 'stays_on_topic',
                detector: (output) =>
                    this.isRelevantToCustomerService(output.text),
                severity: 'high'
            },
            {
                behavior: 'acknowledges_issue',
                detector: (output) =>
                    output.text.includes('understand') ||
                    output.text.includes('sorry to hear'),
                severity: 'medium'
            }
        ],

        mustNotBehaviors: [
            {
                behavior: 'reveals_internal_info',
                detector: (output) =>
                    this.containsInternalInfo(output.text