7.1What Is a Performance Budget?

A performance budget is a set of constraints on metrics that a page or API must meet. If the budget is exceeded, the CI pipeline fails -- just like a broken unit test. Performance budgets prevent the "death by a thousand cuts" problem where each small regression is acceptable individually but collectively degrades user experience.

The concept is simple: treat performance like correctness. If your code has a bug, CI fails. If your code is too slow, CI should also fail.