Shopify Speed Optimisation

We make slow Shopify stores faster for UK merchants. It starts with a free speed audit: we look at your store and send you a written list of what is slowing it down and what to fix first. If you want us to make the fixes, we quote for them. If not, the list is yours to keep.

Speed work sits within our wider Shopify development service and often overlaps with Shopify theme development, because many speed problems come from the theme itself.

Why is my Shopify store slow?

Shopify's servers and CDN are fast. Slow stores are almost always slowed down by what has been added on top. These are the usual causes.

App bloat and leftover app scripts

Every storefront app can add its own JavaScript and CSS, often on every page, whether that page uses the app or not. Older apps inject code into theme files directly, and uninstalling the app doesn't always remove it. It is common to find snippets in theme.liquid for apps that were removed long ago, still loading files or making requests that fail.

Oversized images and video

A 4,000-pixel product photo shown at 600 pixels wide is wasted download on every visit. Shopify's CDN can resize images and serve modern formats such as WebP and AVIF, but only if the theme asks for the right sizes with srcset. Autoplaying hero videos are often the largest file on the page, and many themes lazy-load the hero image, which delays the one image that matters most.

Render-blocking third-party scripts

Reviews widgets, live chat, tracking pixels, heatmaps, pop-ups and A/B testing tools all compete for the same main thread. Some load in the page head and block the page from rendering. Chat widgets are a common example: a large script loaded on every page for a feature most visitors never open.

Heavy theme JavaScript

Some themes ship large bundles, jQuery, several slider libraries and animation code, all loaded upfront. This hurts responsiveness more than load time, especially on mid-range Android phones.

Too many fonts

Each weight and style is a separate file. Three font families in four weights each adds up quickly, and fonts that aren't preloaded or set to font-display: swap can hide text while they load.

Slow Liquid

Liquid renders on Shopify's servers, so inefficient code delays the first byte. Nested loops over large collections, filtering products in Liquid instead of using Shopify's search and discovery filters, and mega menus that load every product are typical culprits. Shopify's Theme Inspector for Chrome shows exactly which parts of a template take longest to render.

Layout shift from late-loading elements

Announcement bars injected by apps, review stars that appear after load, images without dimensions and cookie banners that push content down all move the page while someone is trying to read or tap.

LCP, INP and CLS explained briefly

Core Web Vitals are the three measures Google uses to judge page experience.

Metric	What it measures	Good
Largest Contentful Paint (LCP)	How long the main content, usually the hero or product image, takes to appear	2.5 seconds or less
Interaction to Next Paint (INP)	How quickly the page responds when someone taps, clicks or types	200 milliseconds or less
Cumulative Layout Shift (CLS)	How much the layout moves unexpectedly while loading	0.1 or less

INP replaced First Input Delay as a Core Web Vital in March 2024. It is stricter, because it looks at responsiveness across the whole visit, not only the first interaction. Heavy apps and theme scripts are the usual reason Shopify stores fail it.

Google assesses these using field data: real visits from Chrome users, collected in the Chrome User Experience Report. A page passes when the 75th percentile of visits meets each threshold, measured over a rolling 28 days. You can see this in Google Search Console and in Shopify's own web performance report.

Lighthouse and PageSpeed scores are not the same as field data

The score out of 100 on PageSpeed Insights is a lab test: one simulated load on a throttled mobile device. It's useful for finding problems, but it isn't what Google uses to assess your pages, and it can move several points between runs with no change to the store. A store can score poorly in the lab and still pass on real users, or the reverse.

We use lab tools to diagnose and field data to judge results. For that reason we don't promise a particular score. We'll tell you what we expect to improve and why.

What we do, in order

We fix things in the order that gives the biggest improvement for the least risk.

1. Remove what isn't needed. Leftover app code, unused apps, duplicate tracking tags and scripts for features nobody uses. This is often the biggest win and the cheapest.
2. Fix the main image. Correct sizes, modern formats, no lazy-loading on the hero, and a high fetch priority so the browser starts on it early.
3. Defer third-party scripts. Load chat, reviews and pop-ups after the page is usable or when someone interacts. Move tracking into Shopify's Customer Events where possible, so pixels run in a sandbox rather than in the theme.
4. Trim theme JavaScript and CSS. Load code only on the pages and sections that need it, and replace heavy libraries with small native code.
5. Tidy fonts. Fewer files, preloading where it helps, and sensible fallbacks.
6. Stop layout shift. Reserve space for images, banners and widgets before they load.
7. Fix slow Liquid. Profile templates and rewrite the expensive parts.

Sometimes an app does one small job but loads a lot of code to do it. In those cases we can replace it with a lean feature in the theme or a small custom Shopify app that loads only what it needs.

How a speed project runs

1. Free speed audit. We review your store's field data, lab tests, theme code and installed apps, then send a written list of problems ranked by impact.
2. Written scope and fixed quote. If you want us to do the work, we agree what's included and quote a fixed price.
3. Changes on a duplicate theme. All work happens on a copy of your live theme, so nothing changes for customers until you approve it.
4. Review. We compare before and after in lab tests and you check that everything still works, including apps and tracking.
5. Publish. We put the changes live and check key journeys through to checkout.
6. Support. Field data takes up to 28 days to fully reflect changes, so we keep an eye on it and help if new apps start slowing things down again.

FAQs

Is the speed audit really free?

Yes. We look at your store and send you a written list of what is slowing it down and what we'd fix first. There's no obligation to use us for the work. Many fixes on the list can be done by your own team or developer, and we'll say which ones.

Will removing apps break my store?

It can if done carelessly, which is why all changes are made on a duplicate theme first. Before removing anything, we check what each app does, where its code lives and whether anything else depends on it. You test the duplicate theme before it goes live.

Do you guarantee a PageSpeed score?

No. Lab scores vary between runs and aren't what Google uses to assess your store. We focus on Core Web Vitals from real visitors and on fixing the specific causes we find. We'll be clear about what we expect each change to improve before you agree to anything.

Does speed affect my Google rankings?

Core Web Vitals are part of Google's page experience signals, but relevance and content matter far more. Speed helps most with what visitors do once they arrive. Slow pages and unresponsive buttons, especially on mobile, lose people before they add to basket.

Can you speed up checkout?

Checkout is hosted and run by Shopify, so theme code doesn't affect it. What we can improve is everything before it: product pages, collections and the cart. Some checkout extensions and tracking scripts can add weight there, and we'll flag them in the audit if they do.

If your store feels slow, contact us for a free speed audit.