Speed Optimization Checklist¶
Use this when Core Web Vitals or conversion performance suggests that load speed is hurting the user journey.
Targets¶
| Metric | Good | Needs Work | Poor |
|---|---|---|---|
| LCP | 2500 ms or less | 2501 to 4000 ms | Over 4000 ms |
| INP | 200 ms or less | 201 to 500 ms | Over 500 ms |
| CLS | 0.10 or less | 0.11 to 0.25 | Over 0.25 |
| FCP | 1800 ms or less | 1801 to 3000 ms | Over 3000 ms |
| TTFB | 800 ms or less | 801 to 1800 ms | Over 1800 ms |
Investigation Order¶
- Identify the worst template first: homepage, PDP, collection, cart, or landing page.
- Check mobile before desktop.
- Confirm the LCP element.
- Check whether CLS comes from images, banners, reviews, app widgets, or late product media.
- Check whether INP comes from heavy scripts, app embeds, variant logic, or cart scripts.
Common Fixes¶
- Compress and resize images.
- Serve WebP where appropriate.
- Reserve image, video, review, and app block dimensions.
- Lazy-load below-the-fold media.
- Preload the true LCP image only when it is stable and predictable.
- Remove unused app embeds.
- Defer non-critical scripts.
- Avoid replacing above-the-fold content after load.
CRO Guard-Rail¶
Do not treat speed work as only technical cleanup. Speed changes can alter conversion behavior by changing what users see first, how soon CTAs become usable, and whether app widgets shift content. Record the business metric you expect to protect or improve.