Shopify Case Study: Cutting Mobile LCP by 57% by Fixing a Heavy Hero Image
A common Shopify slowdown: oversized hero media plus app scripts. We reduced LCP, stabilized scores, and added Watchdog alerts to prevent regressions.
Published Sun Jan 11 2026 · Platform: Shopify
Before vs After: Shopify performance case study
A quick “what changed” snapshot you can share with your team.
Before
52
Speed score (0–100)
4.2s
Mobile LCP
After
88
Speed score (0–100)
1.8s
Mobile LCP
Fix guide: the 5 speed killers
Provide your 5 common issues and this template generates a clean remediation guide.
Heavy Hero Image
Fix guideSymptoms
- •LCP element is the hero image/video
- •Large image files, missing responsive srcset/sizes
- •Slow mobile on 4G/3G networks
Fix
- •Compress and convert to modern formats (AVIF/WebP)
- •Serve responsive images with correct dimensions (avoid oversized assets)
- •Preload the LCP image and avoid lazy-loading above-the-fold
- •Replace autoplay hero video with a poster image on mobile
Verify
- •Check LCP element and its transfer size in the audit
- •Confirm correct srcset/sizes and no layout shifts
- •Measure real-device loading and keep Watchdog alerts enabled
Unoptimized JavaScript
Fix guideSymptoms
- •Main-thread long tasks and slow interactivity
- •High Total Blocking Time (TBT) / INP spikes
- •Large bundles loaded on every page
Fix
- •Remove unused code (tree-shake) and split bundles by route
- •Defer non-critical scripts and load third-party tags after interaction
- •Replace heavy libraries with lighter alternatives where possible
- •Audit hydration and eliminate unnecessary client components
Verify
- •Re-run mobile Lighthouse and check TBT/INP improvements
- •Confirm bundle size reduction and fewer long tasks in Performance tab
- •Track regressions with Watchdog after deployments
Third-party scripts
Fix guideSymptoms
- •Performance changes after adding pixels/tags/apps
- •Long network waterfall and blocking requests
- •High CPU time from analytics/trackers
Fix
- •Remove redundant pixels and consolidate tag providers
- •Delay marketing scripts until consent/interaction
- •Use server-side tracking where possible to reduce client load
- •Monitor script changes per release and rollback quickly on regressions
Verify
- •Compare waterfalls before/after and confirm fewer blocking requests
- •Validate conversions/tracking still work after changes
- •Use Watchdog to detect any performance regressions
Render-blocking CSS
Fix guideSymptoms
- •Slow first paint and delayed content rendering
- •Large CSS files and unused styles shipped site-wide
- •Critical content appears late on mobile
Fix
- •Inline critical CSS for above-the-fold content
- •Purge unused styles and split CSS by route/template
- •Avoid large icon fonts; prefer SVG icons
- •Ensure CSS is cached effectively and loaded early
Verify
- •Check render-blocking resources in the audit and waterfall
- •Confirm CSS size drops and first paint improves
- •Track changes with Watchdog across deployments
Too many apps/plugins
Fix guideSymptoms
- •Site gets slower as plugins/apps accumulate
- •Multiple scripts injected on every page
- •Checkout pages become unstable or slow
Fix
- •Remove unused apps/plugins and replace with lighter alternatives
- •Disable scripts on pages where they are not needed
- •Prefer native platform features over app layers when possible
- •Schedule periodic audits after marketing campaigns and theme updates
Verify
- •Measure script count reduction and improved LCP/INP
- •Confirm key features still work (checkout, tracking, search)
- •Set Watchdog alerts to catch future regressions
FAQs
What is a good mobile LCP for a Shopify store?
Aim for ~2.5s or less on representative devices and real-world networks. AuditJet flags regressions and shows which assets are driving LCP.
Do apps really slow down Shopify?
Yes. Many apps inject scripts into pages and checkout. AuditJet helps identify which scripts correlate with performance drops over time.
How does AuditJet prevent future regressions?
Watchdog runs automated scans and alerts you when key metrics (like LCP) degrade, so you can fix issues before conversions drop.