LLM-apps are powerful, but have peculiar characteristics. The non-determinism, coupled with unpredictable, natural language inputs, make for countless ways the system can fall short. Traditional engineering best practices need to be re-imagined for working with LLMs, and LangSmith supports all phases of the development lifecycle. 1) LangSmith helps you develop with greater explainability. With full visibility into the entire sequence of calls, you can spot the source of errors and performance bottlenecks in real-time with surgical precision. 2) LangSmith lets you collaborate with teammates, by providing a Prompt Hub where you can craft, version, and comment on prompts easily. No engineering experience required. 3) LangSmith allows you to add engineering testing rigor, so you can measure quality of your application over large test suites. Layer in human feedback on runs or use AI-assisted evaluation, with off-the-shelf and custom evaluators that can check for relevance, correctness, harmfulness, insensitivity, and more. 4) LangSmith lets you monitor cost, latency, quality of your production application. Spot problems or drift quickly, so you can get back on track as soon as issues arise.