# How should you audit checkout UI extensions for speed?

Source: https://checkoutoptimizelab.com/audit-shopify-checkout-ui-extensions-speed/

List every checkout extension, identify which steps load it, measure its network and main-thread cost, remove unused extensions, and retest checkout completion on mobile.

## 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.