LangChain: How Middleware Lets You Customize Your Agent Harness Without Touching Core Agent Code

LangChain Blog·medium signal

LangChain's latest post details how middleware enables builders to intercept and modify agent behavior at the harness level — the connective layer between LLMs and their environment. The framework supports custom logging, rate limiting, approval gates, and tool-call filtering as middleware, keeping the core agent code untouched. This is the practical implementation guide for the 'Natural-Language Agent Harnesses' concept that's been gaining traction in the agent architecture community.