Start with a repeatable example
Record the page, device, network, login state and time of the problem. Compare the same journey more than once, including an initial visit and a repeat visit. Test on mobile as well as desktop. A fast administrator connection can hide problems experienced by customers.
For example, a slow category filter but a fast static page suggests a different investigation from a large hero image that delays the homepage. Keep the comparison controlled so that a change can be evaluated fairly.
Separate the layers
- Server response: inspect request timings, application errors, slow database queries and external API calls.
- Page loading: inspect image sizes, CSS, fonts and third-party resources.
- Interaction: look for long JavaScript work when customers open filters, search or change variants.
- Layout: check whether images, banners or widgets move content after it appears.
Google’s Core Web Vitals describe loading, responsiveness and visual stability. A Lighthouse run is a lab sample; use real-user field data when available and do not treat one score as a complete diagnosis.
Check caching without risking customer data
Review anonymous HTML and static-asset cache headers, then inspect the reverse proxy and application configuration with server access. Check whether a product or price change invalidates the intended content.
Test anonymous and signed-in sessions separately. Do not solve a low cache hit rate by making cart, checkout or account responses publicly cacheable. A public URL checker cannot verify isolation between customers.
Change one cause, then retest
Reproduce the issue in staging where possible. Compare the same test before and after a change, keep a rollback path and record what was modified. Investigate extensions using profiling and controlled tests instead of disabling them randomly on the live store.
Use the website checker for initial header and HTML observations. If the problem needs application profiling, discuss a Shopware performance audit. The update checklist also helps when slowness starts after a release.