Kastra

The best vibe-coding tools aren't another AI model — they're the open-source Claude Code repos you stack on top of it. The right ones turn the agent from a fancy autocomplete into a disciplined senior engineer: it plans before it codes, designs properly, maps your codebase, and gets scanned for security. Here are eight worth installing.

You don't start by building. You start by finding the one assumption that would kill the idea, then build the smallest thing that tests it. Here's the full idea-to-deployed workflow from a live AI build session: research the market with ChatGPT, pick a segment on unit economics, have AI write the PRD, then vibe-code and ship with Claude Code — in a couple of hours, not a quarter.

A harness is the runtime wrapper that turns a bare language model into an agent — the layer that runs tools, holds memory, assembles context, and enforces limits. The model does the reasoning; the harness does everything the model can't do on its own. It's the part that decides whether you shipped a chatbot or a real agent — and it's why the same model feels brilliant in one tool and useless in another.