About this book:

*App Performance Engineering* is a comprehensive technical guide focused on optimizing the speed, responsiveness, and efficiency of web and mobile applications. The book treats performance as a critical product feature, arguing that user perception of "smoothness"—from the initial second of launch to the battery life at the end of the day—directly impacts business outcomes like engagement and churn. It establishes a rigorous workflow based on the "measure, diagnose, prioritize, fix, and verify" cycle, utilizing tools like Chrome DevTools, Lighthouse, Android Studio, and Xcode Instruments to move from technical traces to concrete optimizations.

The text provides deep dives into platform-specific strategies, such as optimizing the Critical Rendering Path and Server-Side Rendering for the web, and managing cold/warm starts and native memory for mobile. It covers advanced techniques like code-splitting, tree shaking, and lazy loading to minimize bundle sizes, alongside smarter resource loading through protocols like HTTP/3 and Service Workers. Beyond mere speed, the book emphasizes "beating jank" by keeping the main thread free, offloading heavy computations to Web Workers or background threads, and leveraging GPU-accelerated rendering for fluid animations.

A significant portion of the book is dedicated to architectural and organizational health. It explores the performance trade-offs of cross-platform frameworks like React Native, Flutter, and Kotlin Multiplatform, and explains how low-level build optimizations—such as AOT/JIT compilation and Profile-Guided Optimization—can enhance runtime efficiency. It also addresses the critical balance between performance, security, and energy consumption, teaching developers to batch network requests and minimize sensor usage to preserve battery life.

The final chapters move into the operational realm, advocating for a performance-first culture. The book outlines how to set performance budgets and Service Level Objectives (SLOs) that are continuously verified within CI/CD pipelines. By integrating A/B testing to prove the business impact of technical gains and establishing team workflows for triaging regressions, the book provides a durable playbook for maintaining high-performance standards in a fast-paced development environment.

What You'll Find Inside:

• User-centric performance metrics like Core Web Vitals (FCP, LCP, FID) and app start times that measure what users actually experience, not just technical specifications
• A comprehensive profiling toolkit including Chrome DevTools, Lighthouse, WebPageTest, Instruments, and Android Studio for diagnosing performance bottlenecks across web and mobile
• Startup optimization techniques covering critical rendering path, SSR/SSG, resource hints, code-splitting, lazy loading, and platform-specific mobile launch strategies
• Runtime performance strategies for eliminating Jank through main thread scheduling, GPU/CPU trade-offs, efficient animations, and memory management best practices
• Performance sustainability practices including budgets, SLOs, CI/CD verification, A/B testing with guardrails, and team workflows to maintain gains over time

Who's It For:

App Performance Engineering is written for practitioners: web and mobile engineers, tech leads, and product-minded builders who want to turn performance from a firefight into a durable advantage. The book is ideal for those working with JavaScript/TypeScript, Swift, Kotlin, or cross-platform stacks like React Native and Flutter, though the principles are framework-agnostic. Readers should have practical development experience and want to implement measurable performance improvements that impact user engagement and business outcomes.