Relax. We're not going to explain this chapter like a textbook — we'll just talk it through so it's easy to follow.
Let's think about it this way for a second
A vibe check is tasting with a fingertip at the table — it's fast, it's useful, but if you can't repeat it tomorrow, all you're left with is a memory. An eval is the recipe card: same question, same expectation, rerunnable. Whenever you tweak the prompt, tweak the context, or switch models, pull that card back out. Vibe coding is you standing in the loop. An eval is the note you leave behind for when you're not there.
Let's connect it to everyday life
Vibe — open the chat, ask one thing, 'looks good.' Eval — write the question on a card, write the expectation, mark the result pass/fail. Test with a vibe check on day one. If you'll want to reuse it, save it as an eval instead. You don't need a dashboard yet — a single notes file will do. At a restaurant, 'yesterday's dish was good' is a vibe. 'Fish dish, must not be spicy, must satisfy all three guests' is an eval.
Let's try it together
Vibe: “hmm, I like this answer”
Eval: same question tomorrow → pass or fail
Use vibe to explore. Use evals to keep it.You'll be able to tell a vibe check apart from an eval.5-Minute Try-It
List 6 tasks. For each, say whether it needs a vibe check, an eval, or both — and why.
A Quick Word of Caution
Vibe checks are fast. Fast doesn't mean right. If you can't rerun it, it's gone.