LangSmith
Definition
LangSmith makes workflows of LLM applications traceable through execution traces and systematic evaluation.
LangSmith is a platform from LangChain for recording, investigating, and evaluating runs in applications with language models and agents. It combines tracing with offline and online evaluation so teams can compare variants and detect production issues.
Simply explained
Like a flight recorder for an AI application, LangSmith records what happened at each step and then helps compare results. Unlike a flight recorder, however, the tool does not automatically assess the cause.
Why it matters in practice
In automated AI processes, errors often arise only from the interaction of prompt, model, tool, and data. Traces and repeatable evaluations shorten troubleshooting and make quality changes between versions visible.
Example from business
Hypothetical example: A team logs a support agent in LangSmith and tests a new prompt version offline against a curated dataset before it goes into production.
Limits and pitfalls
- Recorded traces may contain sensitive inputs or outputs and therefore require appropriate access, retention, and masking rules. Automatic evaluations also do not replace suitable reference cases or human review for critical decisions.
Origin & history
The documentation distinguishes offline evaluation before deployment from online evaluation on production outputs. Regression tests, backtests, and ongoing quality monitoring serve different purposes.
Use in mid-sized companies
- Possible application in SMEs: A company can secure recurring AI workflows with realistic test cases, centrally investigate error traces, and detect quality drops faster after model or prompt changes.
Frequently asked questions
What is LangSmith used for?
For tracing, troubleshooting, and evaluation of applications with language models or agents.
What is the difference between offline and online evaluation?
Offline tests compare versions before deployment; online evaluation assesses production outputs and looks for quality issues.
Does LangSmith replace human quality assurance?
No, especially for professionally or legally critical results, appropriate references and human review remain important.
Sources
- Evaluation types · LangChain (o. J.): Evaluation types
- Set up LLM-as-a-judge online evaluators · LangChain (o. J.): Set up LLM-as-a-judge online evaluators
Sources checked on 26.10.2026. Editorial use cases are hypothetical; no evidence of real customer results.
Editorially reviewed on: