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LLM observability tools: LangSmith vs Langfuse vs Helicone

Compare LangSmith, Langfuse, and Helicone for LLM tracing, cost monitoring, prompt management, evaluations, gateway workflows, and production debugging.

Updated 2026-06-118 min readIntermediate

Best for

  • Teams debugging LLM applications in production
  • RAG and agent builders who need traces, costs, latency, and evals
  • Developers choosing between hosted, open-source, and gateway observability
  • Product teams tracking model quality regressions

Not for

  • Replacing ordinary application logs and metrics
  • A guarantee that traces alone prevent hallucinations
  • Skipping privacy review before logging prompts and user data

Comparison

Choose by workflow, not brand

OptionBest forStrengthsTradeoffsUse when
LangSmithLangChain, LangGraph, agent tracing, offline evals, production monitoring, and framework-integrated debuggingStrong tracing and evaluation story for LangChain ecosystem apps.Best fit is strongest when your stack already touches LangChain or LangGraph.You need deep traces across chains, tools, agents, and experiments.
LangfuseOpen-source LLM observability, self-hosting, prompt management, datasets, and eval workflowsOpen-source posture with tracing, prompts, evals, and dashboards.Self-hosting means your team owns infrastructure and upgrades if you choose that route.You want observability that can live inside your own environment.
HeliconeGateway-based logging, provider routing, cost tracking, and quick setup across model providersFast integration path through gateway/proxy workflows and unified provider access.Proxy/gateway architecture may not fit every compliance or network setup.You want request logging, usage analytics, and routing with minimal app changes.

What to observe

LLM observability should show the full path from user input to final answer: prompt, retrieved context, model call, tool calls, token usage, latency, cost, error, and evaluator result.

  • Trace retrieval and tool steps, not only the final model call.
  • Capture prompt versions and model routes.
  • Redact sensitive data before storing traces.

Hosted versus self-hosted

Hosted tools reduce operations work. Self-hosted tools can help with data control. The right answer depends on compliance, team size, traffic volume, and how much infrastructure you want to own.

  • Check data retention, redaction, and regional requirements.
  • Estimate trace volume before choosing a plan.
  • Test export paths so you are not locked into one dashboard.

Evals make traces actionable

A trace tells you what happened. An evaluation tells you whether it was good. The best observability setup connects traces to datasets, human annotations, and regression checks.

  • Start with a small golden set of real user questions.
  • Score retrieval and final answer separately.
  • Monitor cost and latency alongside quality.

Decision Rules

A practical checklist

01

Choose LangSmith first if you build with LangChain or LangGraph.

02

Choose Langfuse first if open-source/self-hosting and prompt/eval workflows matter.

03

Choose Helicone first if gateway logging and provider routing are the fastest win.

04

Never log sensitive prompts before defining redaction and retention policy.

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FAQ

Common questions

What is LLM observability?

LLM observability records and analyzes prompts, model calls, tool calls, retrieval steps, costs, latency, errors, and quality signals so teams can debug and improve AI applications.

Is Langfuse better than LangSmith?

Langfuse is attractive for open-source and self-hosting needs. LangSmith is especially strong for LangChain and LangGraph tracing and eval workflows. The better choice depends on stack and compliance needs.

Do I need observability before launch?

Yes for any serious product. Without traces and cost tracking, you cannot reliably debug hallucinations, latency spikes, prompt regressions, or unexpected bills.

Source Links

Primary references used for this guide

Build your own evaluation note

The strongest decision is always local to your workflow. Save the vendor links, define a representative task, record the exact prompt or command, and compare the final evidence instead of the marketing claim.

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