Frontend observability works much like backend observability: get a signal that something is off, investigate it, fix it, then monitor the fix. The hard part is getting those signals at scale. This talk walks through a real investigation where support tickets pointed to a frontend error that didn't make sense at first. Slicing the data by other dimensions didn't explain it. Watching session replays exposed the root cause, which was a browser translation feature rewriting the DOM out from under React. From there, the talk turns from visible failures to experiences that are simply slow. It covers how to define the critical operations in your app, measure their availability and latency, trace slow interactions to the code that causes them, and validate every deploy against your baselines. It closes with how Anthropic ran this loop to make claude.ai roughly 3x faster in two weeks.
This talk has been presented at JSNation US 2026, check out the latest edition of this JavaScript Conference.
