Hey Reader,

It's been a few months since I've written you... and it's because I've been heads-down building. And I finally have something worth sharing.

A developer over on MageChat asked me a fair question recently: when I talk about an "AI harness," do I mean skills, hooks, CLAUDE.md files, ...or something else entirely?

I realized I use the term "AI harness" all the time now, and I've never actually defined it. So here's the full answer.

If you've been building with Claude Code lately, you probably have a pile of parts: a skills folder, a few MCP servers, maybe a 2,000-line CLAUDE.md file you no longer fully trust. The problem isn't the parts. It's that the ecosystem named the parts and never named the whole.

Here's how they fit together:

• Skill -- knowledge the AI pulls in when it's relevant.
• Command -- a thing you invoke on purpose.
• Hook -- something that fires whether you asked or not.
• Plugin -- a bundle of the above, shipped as one unit.
• Harness -- the layer above all of it: what runs, in what order, and what has to be true before work moves forward.

If I needed to sum up what an AI harness is in one sentence, it's: the system that makes an AI follow your process instead of making something up on its own.

And this matters for Magento more than most platforms.

Magento is layered and unforgiving; there always seem to be five plausible ways to do something, and four of them are likely wrong for your specific application. AI is very good at plausible, and that's the risk -- and it's why a harness isn't optional on a codebase like this.

I also recorded a video walking through all of this, if you'd rather watch than read:

​What is an AI harness & why does Magento need one?​

And if you want to see a real harness, HCF (Halt and Catch Fire) is the open source one I built: https://github.com/markshust/hcf​

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One question back, and I'd genuinely love to know:

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Just hit reply... I read every one, and the answers shape what I make next.

Cheers,

Mark Shust Teacher / M.academy Say hi 👋 on LinkedIn & YouTube​