What a harness is and how to build one with Claude Agent SDK

A harness is some code around an AI agent that makes it more effective. Why we've seen people build these specific use case harnesses is sometimes with a specific job, you just wanna micromanage a little bit. You just wanna be more prescriptive about how that job gets done. I'm gonna show you how it works, and then we will talk about how I built it. So the inner face I built for my harness is a terminal UI. The harness core is run on Claude agent SDK, and then it's connected to Real Tools. So it's connected to Sentry, Vercel, and then it's connected to Linear and GitHub in terms of getting tasks done. I think we all have done good work, but then now I've realized that these agents can help us solve very, very specific problems by constraining that work. It's really, like, changed my mind about how work gets done. Everybody's saying it's not the model, it's the harness. But you know what not everybody is saying? What is a harness? In today's How I AI episode, I am going to demystify the idea of a harness, write my own harness, and show you how you can do the same, and explain to you why a custom harness makes sense and could be better than using quad code or codex alone. Let's get to it. This episode is brought to you by bolt.new, the AI app builder for people who have ideas and want to ship them. Most AI tools spit out code that looks great in a demo and falls apart the second you try to do anything real with it, or they lock you into their own platform with no real way out. Bolt is different. You describe what you wanna build, a startup MVP, a landing page, an internal tool, a side project, and Bolt generates production ready code in minutes. Connect Stripe or any other MCP, hook up your domain, and deploy it live. Founders are using Bolt to build businesses doing real revenue. Product managers are shipping prototypes their teams actually use. Designers and marketers are launching campaigns without waiting in line. Anyone can build. Engineering can ship. Everyone wins. You just need an idea and a weekend. Check it out at bolt.new/howiai. Before I get into how to build a harness, let's talk about what a harness is, and I am going to make it as simple as I can for all of you. A harness is some code around an AI agent. Yes. You heard it here first. A harness is just code around an AI agent that makes it more effective. Can that code have AI in it? Sure. Does that code have to have AI in it? Not necessarily. What is the goal of a harness? To make the AI better. It is so simple, and I feel like the way that people have been talking about this have made it such a mystery that I wanted …