In today's fast-paced digital landscape, ensuring the optimal performance of web applications is more critical than ever. As developers, we need robust tools and methodologies to monitor, analyze, and enhance the performance of our applications using data-driven insights. In this talk, I will share my extensive experience in setting Key Performance Indicators (KPIs) for measuring the performance of multiple web apps using browser monitoring tools. I will delve into practical use cases, experience reports, and hands-on demonstrations to provide a comprehensive understanding of the following: - Key Performance Metrics: Identifying and prioritizing the essential KPIs to monitor the health and performance of your web apps. - Data-Driven Performance Optimization: Strategies and best practices for using data to optimize web applications and ensure they meet performance standards. - Setting Alarms: How to configure and manage alarms in browser monitoring tools to proactively address performance issues before they impact users. - Service Level Indicators (SLIs) and Objectives (SLOs): Establishing SLIs and SLOs to set realistic and achievable performance targets. -Practical Implementation: Step-by-step guides and real-world examples of implementing these practices in a production environment. This talk aims to provide a strong practical element, enhancing understanding through real-world examples and hands-on demonstrations. Attendees will leave equipped with the knowledge and tools to take their web application's performance to the next level.