Best LLM Observability & Evals for AI App Builders in 2026
Short answer: The best llm observability & evals for ai app builders in 2026 is Langfuse. The open-source default. Self-host it or use the free cloud tier. Runner-up: LangSmith. Best free option: Langfuse.
Trace, debug and score what your agents do.
#1 Pick
Langfuse
Runner-up
LangSmith
Best free
Langfuse
All llm observability & evals compared
| Tool | Price / free tier | MCP | Open source / local | Verdict |
|---|---|---|---|---|
| Langfuse | Hobby free (50K units/mo, 2 users, 30-day retention); paid tiers above | Unverified | Open source, self-hostable (license not re-checked) | The open-source default. Self-host it or use the free cloud tier. |
| LangSmith | Developer free (5K traces/mo, 1 seat); pay-as-you-go beyond | Unverified | Proprietary | Best if you build on LangGraph. New natural-language trace search. |
| Braintrust | Starter free ($10 model credits, 1 GB, 10K scores, unlimited users, 14-day retention) | Unverified | Proprietary | The strongest eval workflow for teams. |
| MLflow | Free | Unverified | Open source (license not re-checked) | Use it if your ML stack already runs MLflow. |
| Promptfoo ⚠ Pricing not verified | Unverified | Unverified | Open source (license not re-checked) | CLI-first evals and red-teaming that live in your repo. |
"Unverified" means we couldn't confirm it on 2026-10-15. Picks are editorial and never sold.
FAQ
What is the best llm observability & eval in 2026?
Langfuse. The open-source default. Self-host it or use the free cloud tier.
What is the best free option?
Langfuse: Hobby free (50K units/mo, 2 users, 30-day retention); paid tiers above
What is the runner-up?
LangSmith. Best if you build on LangGraph. New natural-language trace search.
How were these picks verified?
Prices and facts were checked against vendor pages or linked sources on 2026-10-15. Rankings are never sold.