# AI agent observability and evaluation tools — The Agents Index

> Source: https://theagentsindex.com/category/observability-evals (curated, re-verified)

Tools to trace, debug, test and evaluate what AI agents do, before and after they ship.

1 agent in this category, A to Z. Each name links to its answer-first markdown twin.

| Name | What it is | Pricing | API |
| --- | --- | --- | --- |
| [LangChain](https://theagentsindex.com/langchain.md) | Open source agent frameworks plus LangSmith, a hosted platform to trace, evaluate, deploy and govern agents. | Free, then $39/seat/month | Yes |