What it is
Diagnosing bugs is a Matt Pocock skill for hard bugs: a disciplined loop of reproduce → form a hypothesis → test it → fix, instead of guessing.
When to use it
- When something is broken and the cause isn't obvious.
- When a fix "should have worked" but didn't.
- When something works locally but not on the live site.
What I typed
Nothing yet. v1 didn't need the full skill. But the agent hit real problems along the way and handled them with the same loop.
What happened
| Symptom | Diagnosis | Fix |
|---|---|---|
| Wizard raced through every question | Run inside the chat with !, which can't press Enter |
Run it in a real terminal |
| Build failed: "uncached data during prerendering" | Next.js 16 needs file reads marked as cacheable | Added "use cache" |
/learn/nope returned status 200, not 404 |
Page streams, and the status is sent before "not found" is known | Documented it and accepted it for v1 |
| A wait-loop never finished | It read the wrong output stream | Fixed the command |
| Preview comment "showed up" on the real site | Two different comments looked alike | Checked both databases: they were separate |
The lesson: look at evidence (logs, the actual database rows) before deciding what's wrong. The last one wasn't a bug at all.