Best LLM Observability Tools (2026)

LLM observability is the practice of monitoring and understanding the behavior of large language model applications in production. It goes beyond traditional application monitoring to cover LLM-specific concerns: tracing multi-step chains and agent workflows, tracking token usage and costs per request, measuring latency across model calls, detecting hallucinations, and evaluating output quality over time.

As LLM applications grow more complex — with RAG pipelines, tool-calling agents, and multi-model routing — observability becomes critical for debugging failures, optimizing costs, and maintaining quality. Tools like Langfuse, LangSmith, and Helicone provide the visibility needed to understand what's happening inside your AI stack.

The right tool depends on your infrastructure and requirements. Here are the key trade-offs:

• Open source vs. managed cloud — Self-hosted tools like Langfuse, Arize Phoenix, and Lunary give you full data control and zero per-event costs. Cloud platforms like LangSmith and Helicone offer faster setup and managed infrastructure, but cost scales with usage.
• OpenTelemetry compatibility — Tools like OpenLLMetry and Arize Phoenix use the OpenTelemetry standard, meaning you can export traces to any OTel-compatible backend. This avoids vendor lock-in and integrates with existing monitoring stacks.
• Framework integration — Most tools offer SDK integrations for LangChain, LlamaIndex, OpenAI, and Anthropic. If you use a specific framework heavily, check which observability tool has the deepest native integration.
• Evaluation capabilities — Some platforms (LangSmith, Braintrust, HoneyHive) include built-in evaluation frameworks for scoring model outputs. Others focus purely on tracing and leave evaluation to external tools.

Pricing for LLM observability tools varies significantly between open-source self-hosted options and managed cloud platforms. Self-hosted tools like Langfuse, Arize Phoenix, and OpenLLMetry are completely free — you only pay for the infrastructure to run them.

Cloud platforms typically offer free tiers with limited event volumes, then charge based on traces or requests. LangSmith starts at $39/seat/month, Helicone at $120/month for growth plans, and Lunary at $30/month. Most enterprise plans offer custom pricing with SSO, SLAs, and dedicated support.

For teams just getting started, self-hosted Langfuse or the free tier of a cloud platform is usually sufficient. As your LLM usage grows, evaluate whether the operational overhead of self-hosting justifies the cost savings versus a managed solution.