Free; Pro Cloud from $19/month
Opik (Comet)
Observability
Open-source LLM observability and evaluation from Comet, with agent tracing, datasets, online scoring, prompt versioning, and optimization.
Observability
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From $20/user/mo
Lunary
Observability
LLM observability platform linking agent traces, chatbot conversations, feedback, prompt templates, and evaluation workflows.
Free tier; Enterprise quote
Traceloop
Observability
LLM tracing, evaluations, and prompt management built around the Apache-2.0 OpenLLMetry SDK. The commercial platform has a free hosted tier and quote-based Enterprise deployment.
Free; Pro from $60/mo Weights & Biases Weave
Observability
LLM observability and evaluation toolkit for tracing AI applications, comparing outputs, and turning failures into repeatable tests.
Helicone
Observability
Proxy-based LLM observability gateway with one-line setup; hosted product in maintenance mode since the March 2026 Mintlify acquisition.
Arize AX
Observability
Enterprise LLM/ML observability (AX) with Phoenix, its ungated open-source tracing and evals core; deep drift and embeddings analysis.
LangSmith
Observability
LangChain's observability and evaluation platform: zero-config LangGraph tracing, CI-gated evals, prompt hub; closed-source SaaS.
Langfuse
Observability
Open-source LLM engineering platform: OpenTelemetry-native tracing, LLM-as-judge evals, prompt management; MIT core with free self-hosting.