LangSmith vs Langfuse

The decision is mostly about coupling and hosting

Both trace LLM applications, store prompts and run evaluations, and the feature comparison converges more each release. What does not converge is the strategic question: one is built alongside a particular application framework and is at its best when you use that framework's abstractions, while the other is deliberately framework-agnostic and self-hostable. If your application is built on that framework, the tighter integration is genuine value rather than lock-in; if it is not, you are paying an integration tax for someone else's model of the world.

The second axis is where the data lives, and it matters more for this category than most. Trace payloads contain your prompts, which routinely contain customer data and occasionally source code. A self-hostable option lets that stay inside your perimeter, which for regulated teams is the difference between a tool being usable and not. For everyone else the managed option removes real operational work, and the honest trade is convenience against where the most sensitive copy of your data ends up.

One practical test cuts through the feature comparison: take a real multi-step run from your system and instrument it in both. Look at whether the resulting trace tells you what you would need during an incident — which step made which call, what it was shown, why it retried. Then check where the payloads landed and who in your organisation can read them. Those two observations usually settle it faster than any evaluation matrix, and both take an afternoon.

Where each one genuinely wins

• —LangSmith genuinely wins if your application is built on the matching framework. The integration is deeper than a generic SDK can be, the abstractions line up, and the time from install to useful traces is short.
• —Langfuse genuinely wins on independence: framework-agnostic instrumentation and a self-hosting path that keeps prompt payloads inside your own environment. If you expect to change frameworks, or cannot send prompts to a third party, that flexibility is the deciding factor.