LangSmith

LangSmith is an observability and evaluation platform built by LangChain, designed specifically for teams developing LLM-powered applications and AI agents. Where general-purpose monitoring tools like Datadog or New Relic focus on infrastructure metrics, LangSmith is purpose-built for the unique challenges of debugging and improving language model pipelines — tracing individual agent runs, inspecting prompt inputs and outputs, and measuring response quality over time.

At its core, LangSmith provides full trace visibility into LLM chains and agent executions. Developers can inspect every step of a multi-turn conversation or tool-calling sequence, which is particularly valuable when debugging unexpected behavior in complex agent workflows. This level of introspection is difficult to achieve with generic logging or APM tools.

Beyond tracing, LangSmith offers an evaluation layer that lets teams define and run automated evals against LLM outputs. Rather than manually reviewing model responses, engineers can build test datasets, run experiments, and track how changes to prompts or models affect output quality over time. This closes the feedback loop between development and production.

Prompt management is another pillar of the platform. Teams can version, compare, and collaborate on prompts directly within LangSmith, treating prompt engineering with the same rigor as code. This is especially useful in organizations where multiple people are iterating on the same prompts.

LangSmith also includes a no-code agent builder, allowing users to prototype agent workflows without writing code — a useful capability for teams that want to experiment with agentic patterns before committing to a full implementation.

In the LLM tooling ecosystem, LangSmith occupies a similar space to platforms like Weights & Biases (Weave), Arize Phoenix, and Helicone. Compared to Helicone, which focuses primarily on API cost and usage tracking, LangSmith provides deeper evaluation and prompt management capabilities. Arize Phoenix is a strong open-source alternative, while Weights & Biases Weave appeals to teams already embedded in the W&B ML experiment tracking ecosystem. LangSmith's tight integration with the LangChain and LangGraph frameworks gives it a natural advantage for teams already using those libraries, though it also supports non-LangChain applications via its SDK.

LangSmith is available as a hosted cloud service with regional options (US Central and EU West), which is relevant for teams with data residency requirements. The platform offers a free tier, making it accessible for individual developers and small teams getting started with LLM application development.