Senior Frontend Performance Engineer

About the role We are looking for a Senior Frontend Performance Engineer to help build one of the fastest web applications in the SaaS market. This is not a standard frontend development role. You will own performance across a large-scale React application, designing advanced rendering and synchronization systems, eliminating production bottlenecks, and building custom performance infrastructure where existing frameworks or libraries are not sufficient. The ideal candidate treats frontend performance as a core product capability and has hands-on experience improving startup time, rendering speed, interaction latency, scrolling performance, memory usage, and the overall responsiveness of complex web applications. About the company Our client is a fast-growing, AI-powered sales engagement platform used by more than 700,000 businesses worldwide. The product helps companies identify prospects, automate outbound communication, and accelerate revenue growth through AI-powered automation, a built-in B2B lead database, and advanced email-deliverability technology. The company operates with a fully remote, globally distributed team and is building technology used at significant scale. What you will do: Own frontend performance across the entire application.Design and implement advanced rendering and data synchronization systems.Identify and eliminate performance bottlenecks in production.Improve application startup time, interaction latency, scrolling, rendering, and perceived performance.Optimize browser memory usage and eliminate UI freezes and rendering jank.Design caching, preloading, lazy-loading, virtualization, and predictive-loading strategies.Build custom performance infrastructure when existing libraries or frameworks are insufficient.Use browser and application profiling tools to investigate complex performance issues.Collaborate with product and engineering teams to ensure new features meet performance standards.Establish performance benchmarks, monitoring systems, and engineering best practices.Benchmark the application against some of the fastest SaaS products on the market. What we are looking for: At least 4 years of professional frontend engineering experience.At least 4 years of experience building large-scale React applications used by thousands of users.Experience building, maintaining, or scaling a product used by at least 100,000 monthly active users.Strong experience with React, TypeScript, JavaScript, and modern browser APIs.Proven experience significantly improving frontend performance in production.Deep understanding of browser internals, rendering pipelines, the event loop, memory management, and JavaScript performance.Experience with caching, virtualization, lazy loading, preloading, state management, and data synchronization.Strong hands-on experience with Chrome DevTools or similar profiling and performance-analysis tools.Experience building custom frontend infrastructure, internal frameworks, or performance tooling.Strong computer science fundamentals, including data structures and algorithms.Experience working on products where speed and responsiveness were important business objectives.High engineering standards and strong attention to detail.Professional English communication skills. Role details Work model: Fully remoteLocation: EuropeWorking hours: Overlap with European business hoursBudget: USD 7,000–12,000 per monthLanguage: English