When an application crashes in production, you need to know exactly what happened, to whom, and on what line of code. Sentry remains the gold standard for error tracking and performance monitoring. By simply adding their SDK to your frontend or backend, Sentry automatically captures unhandled exceptions, attaches the user's browser details, network requests leading up to the error, and un-minifies the stack trace using your source maps.
Sentry has recently evolved beyond just error tracking to full-scale performance monitoring, helping identify slow API endpoints and N+1 database queries. Their Session Replay feature is particularly magical, recording a video-like reproduction of the DOM exactly as the user saw it when the error occurred, completely eliminating the "cannot reproduce" back-and-forth. The primary drawback is that the sheer volume of features can make the dashboard overwhelming for beginners, and misconfiguring your sample rates can quickly blow through your quota.