Overview

Exp - 7 years

We are seeking an immediate-impact Senior Web Performance Engineer focused exclusively on client-side application performance, Core Web Vitals, and digital customer experience across our large-scale retail e-commerce platform. This is a hands-on contractor role for a specialist who can contribute from Day 1 with zero training ramp-up. You will be responsible for identifying, analyzing, and driving the remediation of client-side bottlenecks affecting customer experience, conversion, and revenue. You will own our digital experience monitoring (DEM) telemetry, translating complex browser behavior and third-party script impacts into actionable technical solutions.

Key Responsibilities

• Client-Side Monitoring & Optimization
• Core Web Vitals Ownership: Continuous tracking, debugging, and remediation of client-side user experience metrics: LCP (Largest Contentful Paint), INP (Interaction to Next Paint), and CLS (Cumulative Layout Shift).
• Browser Critical Path Analysis: Analyze browser rendering lifecycles, DOM/CSSOM construction, layout thrashing, resource prioritization, and main-thread execution bottlenecks.
• Digital Experience Telemetry: Manage, configure, and maximize our client-side monitoring ecosystem to identify user friction patterns, rage clicks, and performance anomalies before they impact revenue.
• Telemetry Correlation: Leverage observability platforms to directly correlate server-side operational metrics (like $TTFB$) with end-user browser experience and rendering trends.
• Engineering Partnership: Partner closely with frontend feature teams to review remediation plans, validate code fixes, establish performance budgets, and prevent release-over-release regressions.

Required Skills

• Enterprise E-Commerce Scale: Proven experience optimizing high-traffic, transactional retail web applications with complex third-party tag environments.
• Core Web Vitals Expertise: Deep, production-tested understanding of how client-side user metrics are captured, debugged via Chrome DevTools, and optimized.
• Digital Experience Monitoring (DEM) Stack: Strong hands-on experience with at least two of the following or their direct market equivalents:
  • Synthetic Monitoring: Catchpoint, WebPageTest, Lighthouse CI
  • Real User Monitoring (RUM): Blue Triangle, SpeedCurve, Akamai mPulse
  • Session Replay & Behavior: ContentSquare, FullStory, Quantum Metric
  • Tag/Performance Optimization Platforms: Yottaa
  • Application Performance Monitoring (APM): New Relic, Datadog (Client/RUM views)
• Browser Diagnostics: Expert-level ability to read network waterfalls, interpret filmstrips, profile JavaScript execution long-tasks, and analyze bundle allocations.
• Frontend Architectural Literacy: Deep conceptual and diagnostic understanding of modern JavaScript frameworks (e.g., React rendering behavior, state reconciliation, and server-side rendering hydration impacts) to effectively collaborate on code-level fixes with developers.

What We Are NOT Looking For (The Screening Gates)

• The Pure Backend Tester / Load Generator: Engineers whose core strength is writing server-side load test scripts (JMeter, BlazeMeter, Gatling) with no deep browser profiling experience.
• The Traditional Infrastructure SRE: Candidates focused on Kubernetes orchestration, cloud network topology, database scaling, or infrastructure uptime.
• The Pure Feature Developer: Frontend UI developers whose primary history is building consumer-facing web features and who only view performance as an afterthought or automated Lighthouse checklist.
• The Passive Dashboard Reporter: Individuals who can build a chart in New Relic or Splunk but lack the deep client-side technical knowledge to find the root cause and drive code-level remediation.