LLM Observability & Evals
LLM observability and evaluation platforms — tracing, monitoring, evals, and testing for LLM apps and AI agents. Compare Langfuse, LangSmith, Braintrust, Arize, and the tooling teams use to ship reliable AI.
Our editors' top LLM Observability & Evals picks for 2026 are Langfuse (best for Open-source default for tracing, evals, and prompt management), LangSmith (best for Deep agent tracing if you live in the LangChain ecosystem), and Braintrust (best for Turning production traces into evals that gate releases). All 25 tools in this category are hand-reviewed and re-checked each edition — the full ranked directory is below.
Where to start
AcquiredLangfuse
AI Infrastructure
Freemium
4.84
174
LangSmith
AI Infrastructure
Freemium
4.86
400
Braintrust
AI Infrastructure
Freemium
4.81
256
Arize AI
AI Infrastructure
Paid - $100 /mo
4.8
335
Patronus AI
Developer Tools
Paid - Inquire
4.78
237
Helicone
Developer Tools
Paid - $80 /mo
4.75
225
Sorted by
LangSmith
AI agent observability platform — tracing, monitoring, and evals for any agent stack.
Freemium
4.86
400
Arize AI
ML observability platform for monitoring and fine-tuning machine learning models.
Paid - $100 /mo
4.8
335
Arthur
ML Observability platform ensuring transparent, compliant, and efficient AI operations.
Paid - Inquire
4.82
312
AgentOps
Agent observability platform for OpenAI, CrewAI, Autogen, and 400+ LLMs. Visually track LLM calls, tools, multi-agent flows. Rewind and replay runs.
Freemium
4.84
293
AcquiredWeights & Biases
Central dashboard for tracking hyperparameters, metrics, and ML workflows.
Paid - Inquire
4.82
274
Coval
Simulation and observability platform that tests, monitors, and evaluates AI voice and chat agents.
Free Trial
4.84
262
Braintrust
AI evals and observability — turn production traces into evals and ship quality AI at scale.
Freemium
4.81
256
Phoenix by Arize
Open-source LLM and agent observability with tracing, evaluations, and experiment tracking.
Free
4.82
255
Judgment Labs
Judgment Labs is a continuous-improvement stack for AI agents — monitoring, failure analysis, and pre-deploy testing.
Paid - Inquire
4.83
245
Patronus AI
Automated LLM and agent evaluation platform — detect hallucinations, bias, and performance regressions.
Paid - Inquire
4.78
237
Okareo
Simulation testing for voice and text AI agents: synthetic users, audio-condition evals, CI/CD gating.
Free Trial
4.84
234
Helicone
Helicone: Open-source monitoring for generative AI applications.
Paid - $80 /mo
4.75
225
Fiddler AI
Fiddler AI: AI Observability platform for ML model monitoring and explainability.
Paid - Inquire
4.75
225
Klu
Generative AI app platform — design, deploy, and optimize LLM-enabled applications with collaborative prompt management, experiments, and evals.
Freemium
4.75
215
HoneyHive
Optimization platform for GPT-4 applications, enhancing production LLM apps with observability, evaluation, and fine-tuning tools.
Paid - Inquire
4.73
210
Athina AI
Full-stack LLMOps platform — prototype pipelines, run evals, detect hallucinations and safety issues in LLM products. 50+ preset evals, YC-backed.
Freemium
4.72
205
Galileo
Galileo is an LLM evaluation and observability platform that tests, monitors, and guardrails GenAI applications and agents at enterprise scale.
Freemium
4.75
180
AcquiredLangfuse
Open-source LLM engineering platform — tracing, evals, prompt management, and metrics.
Freemium
4.84
174
Kolena
AI quality platform for end-to-end testing, data curation, and model evaluation.
Paid - Inquire
4.62
170
Deepchecks
Continuous ML validation platform for testing, CI/CD, and monitoring.
Paid - Inquire
4.64
170
Distributional
Distributional is an enterprise AI testing platform that statistically detects drift and regressions in agents and LLM applications before they hit product
Paid - Paid
4.73
150
Freeplay
Freeplay is an LLM evaluation and observability platform that helps cross-functional teams test, monitor, and improve AI-powered products.
Paid - Paid
4.61
120
Pay-i
Pay-i is the AI cost observability and governance platform tracking spend across OpenAI, Anthropic, Google, and self-hosted models. Khosla Ventures-backed.
Paid - Paid
4.49
100
Openlayer
Openlayer is the LLM and ML observability platform for testing, monitoring, and improving AI models in production. YC alum; ~$5M seed.
Freemium
4.48
95
TruEra
ML monitoring, testing, and quality management solutions for AI.
Paid - Inquire
4.59
92
LLM Observability & Evals AI, answered
What is LLM observability?
LLM observability is watching what your AI application actually does in production — logging every model call with its prompt, response, latency, and cost, tracing multi-step agent runs, and flagging failures like hallucinations or refusals. It answers "why did the model do that?" the way APM tools answer it for ordinary software.
What are LLM evals?
Evals are repeatable tests for AI quality: you run a model or agent against a dataset of cases and score the outputs — with exact checks, rubrics, or an LLM acting as judge. Teams run evals before shipping prompt or model changes, the way traditional teams run test suites, so quality changes are measured rather than guessed.
Do I need separate tools for observability and evals?
Increasingly, no. The category has converged: platforms like Langfuse, Braintrust, LangSmith, and Galileo do both, because the workflows feed each other — production traces become eval datasets, and eval scores get monitored in production. Standalone point tools remain for specialized needs like cost tracking (Pay-i) or voice-agent simulation (Coval, Okareo).
How is this different from traditional ML monitoring?
Traditional ML monitoring (Arize, Fiddler, Arthur) watches structured models for drift and data quality against ground-truth labels. LLM workloads add open-ended text, multi-step agent traces, and no single right answer — so the tooling adds tracing, LLM-as-judge scoring, and prompt versioning. The older ML platforms have all added LLM features, while a new generation was built LLM-first.
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