LangSmith

LangSmith is an observability and evaluation platform for LLM applications, covering traces, datasets, A/B testing, and feedback collection.

It traces LLM calls and chains, lets you build and manage datasets for evaluation runs, compares experiments through A/B testing, and gathers both human and programmatic feedback on outputs.

It suits teams running LLM apps that need to inspect and evaluate behavior in one place. It is less suitable if you need self-hosting or want to avoid vendor lock-in: it is not open source, the standard tiers are not self-hostable, and the free tier caps traces and seats, so production scale requires a paid plan. Its features are also tightly coupled to the LangChain ecosystem.

Compared with other LLM observability tools, it is the LangChain-aligned, hosted option, pairing tracing with built-in evaluation and feedback rather than tracing alone.