A practical site speed checklist for Shopify stores

Most slow Shopify stores didn't get slow on purpose. We audit stores that launched fast and lost it one app, one tag and one hero banner at a time. Nobody noticed, because each change looked small.

The fix is a checklist you repeat, not a one-off rescue. Measure with real visitor data first. Then work through apps and third-party scripts, images, theme sections, fonts and large collections, in that order. Recheck every month so the gains stick.

Where should you start measuring?

Start inside Shopify, not with a one-off test. In the admin, go to Analytics > Reports and search for "contentful", "next" or "cumulative". That brings up the web performance reports for the three Core Web Vitals.

Shopify's performance overview explains what each one measures and what counts as good.

• Largest Contentful Paint (LCP) is how fast the main content appears. Good is within 2.5 seconds.
• Interaction to Next Paint (INP) is how quickly the page responds to taps and clicks. Good is under 200 milliseconds.
• Cumulative Layout Shift (CLS) is how much the page jumps around as it loads. Good is under 0.1.

These reports use real visitor data, so they reflect your customers' actual phones and connections. They break results down by page type and by URL. Numbered markers on the chart flag changes such as app installs and theme updates, which makes it far easier to see what caused a dip.

Apps and third-party scripts

This is where we find the biggest wins on most stores. Every review widget, chat bubble, upsell tool and tracking pixel adds code the browser has to load. Shopify's own guidance is to check that each app creates enough value to offset any performance cost.

Work through this list with whoever owns marketing.

1. List every installed app and what it does for sales today.
2. Remove the ones nobody can defend. Then check the theme for leftover snippets, because uninstalling doesn't always clean up.
3. Open your tag manager and remove unused or low-value tags. Old campaign pixels are common.
4. Look for two apps doing the same job, such as two review tools or two popup builders.
5. Ask whether a native Shopify feature now covers what an app used to do.

Slow responses to taps, the problem INP measures, usually trace back to JavaScript. On the stores we see, that's more often apps and tags than the theme itself.

Images, fonts and theme sections

Images are the most common reason LCP slips. A hero image uploaded straight from a photoshoot at full size will always be slow on a phone.

• Resize images to the size they display at. Shopify recommends JPG for photos and PNG for graphics that need transparency.
• Keep the first image on each template simple. A carousel of five large slides at the top of the page costs more than it earns.
• Give images fixed dimensions so the layout doesn't jump when they load. That protects CLS.
• Limit custom fonts to the weights you actually use. Each extra weight is another file.
• Watch the number of sections. Shopify notes that a high number of sections on a template can reduce performance, and animations deserve a test before they go live.

Theme age matters too. Shopify points out that its Horizon family and Online Store 2.0 themes are free and optimised for performance. If you're on a heavily modified older theme, a rebuild can cost less than years of patches. That's often the first question in our design and build work.

Do large collections slow Shopify down?

They can. A collection page trying to load hundreds of products at once is heavy on any phone. Shopify suggests turning on pagination for large collections, so fewer products load at one time.

We see this most on big catalogues with deep filtering. Collectors, trade buyers and fashion customers all browse this way. The answer is rarely fewer products. It's a page that loads what the customer needs first, with filters that work properly on mobile.

Search and filtering apps deserve the same scrutiny as any other app. They sit on your highest intent pages, so a slow one hurts more than most.

How do you stop speed slipping again?

Speed isn't a project with an end date. The store keeps changing, so the checks have to keep happening.

A simple rhythm works well.

• Check the web performance reports monthly, and after any app install or theme release.
• Agree a rule that new apps get a short speed review before they go live.
• Test larger theme changes before every visitor sees them. Shopify Rollouts let you schedule a change and A/B test it against the live theme.
• Plan quiet periods around peak trading, the way we describe in our Black Friday checklist.

Most stores we look after don't need a big speed project. They need someone watching the numbers and fixing things while they're small. If conversion rate shifts with no change on the store, our note on how Shopify measures sessions explains one common cause. We cover that rhythm in what ongoing Shopify support should include.

Where parallel helps

Speed work sits inside our Shopify support packages, which start at £400 a month. One improvement is a focused piece of work, such as speeding up a slow template or clearing out an old app. For stores with a longer backlog, the Growth subscription opens with an audit of theme, apps, site speed and analytics. Then we work through fixes against a KPI baseline.

If your store feels slower than it did at launch, book a call and we'll go through the reports with you.