LangSmith alternatives for tracing prompts and tool calls

Here are solid LangSmith alternatives for tracing prompts, LLM calls, and tool/function calls, grouped by what they’re best at:

Managed observability platforms

These are the closest to LangSmith in terms of end-to-end tracing, debugging, and evaluation.

• Helicone

  • OpenAI-compatible proxy for logging/tracing LLM requests
  • Good dashboards, cost tracking, latency, prompt history
  • Easy to add to many stacks

• Arize Phoenix

  • Strong for LLM observability and evaluation
  • Great for tracing, embeddings, retrieval/debugging, and experiments
  • Open-source, can self-host

• OpenTelemetry + vendor backend

  • If you want full control, instrument with OTel and export to:
    • Datadog
    • Honeycomb
    • Grafana Cloud
    • New Relic
  • Best if you already use standard observability tooling

• WhyLabs

  • Focus on monitoring, drift, and production observability
  • Useful for model/application monitoring at scale

• Traceloop

  • LLM tracing built around OpenTelemetry
  • Good for distributed traces across app, model, retrieval, and tools

• Braintrust

  • Strong for prompt testing, evals, and experiment tracking
  • Also supports tracing and collaboration

Open-source / self-hostable

Good if you want more control, lower cost, or local deployment.

• Arize Phoenix

  • Open-source leader here
  • Best mix of tracing + evaluation + retrieval analysis

• OpenLLMetry

  • OpenTelemetry-based instrumentation for LLM apps
  • Works well as a standard tracing layer

• Langfuse

  • Very popular LangSmith alternative
  • Traces, prompt management, scores, evals, user feedback
  • Self-host or cloud

• Opik

  • Tracing and evals for LLM apps
  • Good developer experience and prompt/version tracking

If your main goal is just tracing tool calls

If you want to trace agent steps, tool invocations, and nested spans, these are especially relevant:

• Langfuse
• Arize Phoenix
• Traceloop
• OpenTelemetry with any backend
• Datadog / Honeycomb if you already have infra tracing

Quick recommendations

• Best overall replacement for LangSmith: Langfuse
• Best open-source observability + evals: Arize Phoenix
• Best if you want standard distributed tracing: OpenTelemetry / OpenLLMetry
• Best if you want simple logging/proxy for OpenAI calls: Helicone
• Best for prompt testing/evals and team workflows: Braintrust

What to choose by use case

• Debugging one app with tool calls: Langfuse or Phoenix
• Enterprise tracing with existing infra: OpenTelemetry + Datadog/Honeycomb
• Prompt engineering and eval-heavy workflows: Braintrust or Langfuse
• Retrieval-augmented systems: Phoenix
• Low-friction OpenAI request logging: Helicone

If you want, I can also give you a feature comparison table for these tools, or narrow it down based on your stack, like Python/LangChain/LlamaIndex/OpenAI/agents.