The Agentic Journal

Writing

What I learn building agents, and why it matters

01
Agent EvaluationMarch 202612 min read

How LangChain Builds Evals for Deep Agents

The best agent evals directly measure agent behavior that matters. Here is how the LangChain team sources data, creates metrics, and runs well-scoped, targeted experiments over time to make agents more accurate and reliable.

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TL;DR

The best agent evals directly measure agent behavior that matters. Here is how the LangChain team sources data, creates metrics, and runs targeted experiments to make agents more accurate and reliable.

02
Agent EngineeringMarch 202610 min read

How Middleware Lets You Customize Your Agent Harness

LangChain built a middleware system for Deep Agents that lets developers intercept and customize any part of the agent lifecycle, from before the first model call to after the final result, without modifying core agent logic.

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TL;DR

Agent middleware gives developers precise control over logging, retries, guardrails, and tool behavior by hooking into defined lifecycle points. Here is how LangChain designed it.