SentryTooling & Quality

It tells you what actually broke on the live site, not just in someone's browser. You add a small piece of code and it catches every crash together with what the user was doing, groups hundreds of them by likely cause and links each group to the version that introduced it — so a regression reaches you by email instead of from a customer. It also times requests and watches the code as it runs, which shows where the slowness really comes from.