Demo Magic
ELI5 - The Vibe Check
You've run this feature ten times and it's been broken nine of them, but right now, in front of the client, on the one run that matters, it works perfectly. Demo magic is the unexplainable, unrepeatable phenomenon where flaky AI-generated code chooses the worst possible moment to behave, and you decide not to question it out loud.
Real Talk
Demo magic refers to the often illusory reliability of a feature specifically during a live demonstration, despite known flakiness in other runs, common with AI-generated code or agent behavior that varies between executions. Experienced developers treat it with suspicion rather than relief, since a demo that only works once tells you nothing about whether it will work again.
When You'll Hear This
"It's demo magic, don't touch anything until the meeting's over." / "That's not a fix, that's demo magic, it'll break again the second we're offline."
Related Terms
Flaky Test
A flaky test is a test that sometimes passes and sometimes fails for no clear reason — even when nothing changed.
Happy Path
The happy path is when everything goes perfectly — the user types the right thing, the API responds correctly, nothing breaks.
Heisenbug
A bug that disappears when you try to find it. Named after Heisenberg's uncertainty principle — the act of observing (debugging) changes the behavior.
Vibe Check
A vibe check in dev culture is when you step back and ask 'does this feel right?' before shipping.
Works on My Machine
The most dangerous phrase in software development.