# What performance evidence should you compare before choosing a Shopify theme?

Source: https://themerankweekly.com/compare-shopify-theme-performance-evidence/

Compare the same home, product, and collection templates under the same test conditions, then review LCP, INP, CLS, TTFB, and the JavaScript and image work behind them.

## Start with the likely cause

Use the gap between TTFB, FCP, LCP, CLS, and INP to narrow the problem before changing code. Keep the template, device, and network conditions consistent.

## Change one thing on a theme copy

Isolate the suspected image, Liquid, CSS, JavaScript, app, or extension cost. A single controlled change makes the result easier to interpret and reverse.

## Verify the whole journey

Repeat the measurement, then test navigation, product selection, cart updates, and checkout handoff. A faster metric is not a win if the storefront task breaks.

## Source

[Shopify developer documentation](https://shopify.dev/docs/storefronts/themes/best-practices/performance), accessed September 21, 2026.

## Frequently asked questions

**What should be measured?**
:   Use the metric tied to the suspected cause, then verify the complete task.

**Where should the change be tested?**
:   On a theme copy with repeated conditions.

**When is the work complete?**
:   After the live journey and the repeated measurement pass.