Choosing an LLM Evaluation Tool: The Complete Comparison

Promptfoo, RAGAS, DeepEval, TruLens, LangSmith—which one should you use?

In this guide, I'll compare the top 5 evaluation frameworks and help you choose.

The 5 Tools Compared

Tool	Best For	Cost	Learning Curve
Promptfoo	General LLM testing	Free (OSS)	Easy
RAGAS	RAG systems	Free (OSS)	Moderate
DeepEval	Production monitoring	Free tier	Moderate
TruLens	LangChain apps	Free tier	Easy
LangSmith	LangChain ecosystem	$39/mo	Easy

Tool #1: Promptfoo

Best For

• General LLM evaluation
• Prompt engineering
• Model comparison
• CI/CD integration

Key Features

• 200+ built-in test types
• Beautiful HTML reports
• Model A/B testing
• Red team tests included
• YAML config (easy to learn)

Example Use Case

"I want to test 50+ queries against GPT-4 and Claude, compare outputs, and catch regressions."

Pricing

• Free: Unlimited local use
• Team ($50/mo): Collaboration features

Verdict

✅ Best general-purpose tool. Start here if you're new to LLM evaluation.

Tool #2: RAGAS

Best For

• RAG system evaluation
• Retrieval quality testing
• Research/academic use

Key Features

• Context Precision, Recall, Faithfulness metrics
• Designed specifically for RAG
• Python-first (good for ML engineers)
• Integrates with HuggingFace

Example Use Case

"I need to measure retrieval accuracy and answer grounding for my RAG chatbot."

Pricing

• Free: Open-source Python library

Verdict

✅ Best for RAG-specific evaluation. Use alongside Promptfoo for comprehensive coverage.

Tool #3: DeepEval

Best For

• Production monitoring
• Real-time evaluation
• Hallucination detection
• Unit testing for LLMs

Key Features

• 14+ evaluation metrics (hallucination, toxicity, bias)
• Pytest integration
• Production dashboard
• Custom metrics support

Example Use Case

"I want unit tests for my LLM and real-time hallucination monitoring in production."

Pricing

• Free: Up to 5K evaluations/month
• Pro ($99/mo): 50K evaluations, team features

Verdict

✅ Best for production monitoring. Great if you want real-time alerts.

Tool #4: TruLens

Best For

• LangChain applications
• Tracing and debugging
• Explainability

Key Features

• Built-in LangChain integration
• Visual trace viewer
• Feedback collection
• Ground truth comparison

Example Use Case

"I'm using LangChain and need to debug why my chain is failing."

Pricing

• Free: Open-source
• Enterprise: Custom pricing

Verdict

✅ Best for LangChain users. Seamless integration.

Tool #5: LangSmith

Best For

• Teams heavily invested in LangChain
• Debugging production issues
• Dataset management

Key Features

• Official LangChain tool
• Trace viewer
• Dataset versioning
• Collaboration features
• Hosted solution

Example Use Case

"We use LangChain in production and need a hosted evaluation platform."

Pricing

• Developer ($39/mo): 1 user, 50K traces
• Team ($199/mo): 5 users, 200K traces

Verdict

⚠️ Best if you're all-in on LangChain. Otherwise, use Promptfoo (cheaper).

Feature Comparison Matrix

Feature	Promptfoo	RAGAS	DeepEval	TruLens	LangSmith
General LLM testing	✅	❌	✅	✅	✅
RAG-specific metrics	⚠️	✅	⚠️	⚠️	⚠️
Red team tests	✅	❌	✅	❌	❌
Production monitoring	❌	❌	✅	✅	✅
CI/CD friendly	✅	✅	✅	⚠️	⚠️
Easy to learn	✅	⚠️	⚠️	✅	✅
Free tier	✅	✅	✅	✅	❌

My Recommendations

🏆 For Most Teams: Promptfoo + RAGAS

• Promptfoo: General evaluation, red teaming, CI/CD
• RAGAS: RAG-specific metrics
• Cost: $0 (both open-source)
• Setup time: 1-2 hours

🚀 For Production Monitoring: DeepEval

• Real-time hallucination detection
• Alerting and dashboards
• Great for high-stakes apps

🔗 For LangChain Users: TruLens or LangSmith

• TruLens: Free, good for debugging
• LangSmith: Paid, full-featured

Quick Start Guide

Week 1: Set Up Promptfoo

Week 2: Add RAGAS (if using RAG)

Week 3: Set Up DeepEval (for production)

Conclusion

TL;DR:

• Start: Promptfoo (easiest, free)
• RAG systems: Add RAGAS
• Production: Add DeepEval
• LangChain users: Consider TruLens or LangSmith

You don't need to choose just one—use multiple tools for different purposes.