How to Build a Custom Agent Harness

An agent harness is the scaffolding that connects a language model to the real world, determining how effectively the agent completes tasks. LangChain’s create_agent provides a minimalist framework for building custom harnesses, with middleware serving as composable building blocks that hook into the agent loop to add capabilities like context management, memory, tool handling, and policy enforcement. Task-harness fit–ensuring the harness matches the specific demands of the agent’s mission–is crucial for building agents that perform well in production environments.