CONTENT:

Core Web Vitals Recovery: How Simulation Identified Hidden Performance Bottlenecks

An e-commerce site struggling with Core Web Vitals scores despite technical optimization efforts used traffic simulation to identify performance bottlenecks that lab testing had missed. This case study examines how simulation-based testing revealed the gap between lab data and real-user experiences.

The Challenge

The site's lab-based CWV testing showed passing scores, but real-user monitoring data showed failing scores for LCP and CLS. The engineering team couldn't reproduce the issues reported by real users, making optimization impossible.

The Solution

The team ran traffic simulation campaigns that generated real browser sessions across different device types, network conditions, and geographic locations, capturing field-level performance data that lab tests missed.

The Results

Simulation identified 3 specific performance bottlenecks: a third-party script loading differently across regions, an image optimization issue affecting mobile users, and a CLS issue triggered by specific browsing patterns. After remediation, the site achieved passing CWV scores across all metrics and device types.

Key Takeaways

Traffic simulation bridges the gap between lab-based and field-based CWV testing, identifying performance issues that affect real users but don't appear in controlled test environments.