End-to-end latency estimation in web applications is crucial for system operators to foresee the effects of potential changes, helping ensure system stability, optimize cost, and improve user experience. However, estimating latency in microservices-based architectures is challenging due to the complex interactions between hundreds or thousands of loosely coupled microservices. Current approaches either track only latency-critical paths or require laborious bespoke instrumentation, which is unrealistic for end-to-end latency estimation in complex systems.