Best LLM Observability & Eval Tools in 2026
Once an LLM feature ships, the questions change from "does it work" to "why did it say that" and "did the new prompt make it worse". Here are the leading tracing and evaluation tools in 2026, and the open standard underneath them, compared on pricing model, self-hosting and how well they handle agents.
LLM Observability & Evals Tools Compared
| Tool | Pricing | Free tier |
|---|---|---|
| Langfuse | Free · paid from $29/mo | |
| Braintrust | Free · paid from $249/mo | |
| OpenTelemetry | Free | |
| LangSmith | Free · paid from $39/seat/mo |
The Best LLM Observability & Evals Tools, Ranked
1. Langfuse
Free tier· Free · paid from $29/moOpen-source LLM tracing, evals and prompt management: MIT-licensed, self-hostable, and $29/month in the cloud with unlimited users.
- Genuinely open source and self-hostable
- Unit pricing does not punish adding teammates
- Framework-agnostic: OpenTelemetry, LangChain, LlamaIndex, raw SDKs
2. Braintrust
Free tier· Free · paid from $249/moEval-first AI observability with unlimited users on every plan. It is priced on data processed and scores run, not seats.
- Strongest eval and experiment workflow in the category
- Unlimited users, so PMs and domain experts can review outputs
- Generous startup program
3. OpenTelemetry
Free tier· FreeThe vendor-neutral standard for traces, metrics and logs, with GenAI conventions that describe LLM calls, agents and MCP in one shared schema.
- No vendor lock-in: switch backends without re-instrumenting
- One trace spans your API, database and model calls
- Every serious observability vendor accepts OTLP
4. LangSmith
Free tier· Free · paid from $39/seat/moLangChain's tracing and evaluation platform, the deepest fit for LangGraph agents. It is priced per seat plus per trace.
- Best-in-class visibility into LangGraph and LangChain agents
- Mature evals, datasets and annotation queues
- Accepts OpenTelemetry traces from non-LangChain code
How to choose a llm observability & evals tool
- Instrument with OpenTelemetry first if you can. Every tool here ingests it, so switching later costs a config change rather than a rewrite.
- Choose Langfuse if you need to self-host or keep data in your own cloud. It is MIT-licensed, and the cloud prices by usage rather than seats.
- Choose LangSmith if your agents are built on LangGraph or LangChain, where its traces need no extra instrumentation.
- Choose Braintrust if evals are the main job and non-engineers need to review outputs. Every plan has unlimited users.
- Model trace volume before you pick. Agent runs produce many spans each, and every pricing model here scales with them.
Frequently Asked Questions
What are the best llm observability & evals tools for startups in 2026?⌄
The best llm observability & evals tools for startups in 2026 include Langfuse, Braintrust, OpenTelemetry, LangSmith. Compare them by pricing, free tiers, and features in the list above.
What is the best free llm observability & evals tool?⌄
Free llm observability & evals options include Langfuse, Braintrust, OpenTelemetry, LangSmith — all offer a free tier suitable for bootstrapped startups and MVPs.
How do I choose a llm observability & evals tool?⌄
Start with your budget and team size, prefer tools with a free tier to validate, and make sure your pick integrates with the rest of your stack. App Stack Builder can recommend a complete, budget-aware stack in about 60 seconds.
Need the whole stack, not just llm observability & evals?
Get a free, AI-powered tech stack — matched to your budget, app type, and team size in 60 seconds.
Build my stack free