Report Summary

  • 33

    Performance

    Renders faster than
    53% of other websites

  • 81

    Accessibility

    Visual factors better than
    that of 52% of websites

  • 75

    Best Practices

    More advanced features
    available than in
    36% of websites

  • 84

    SEO

    Google-friendlier than
    53% of websites

costco.co.uk

Join the club & start saving! | Costco UK

Page Load Speed

3.6 sec in total

First Response

293 ms

Resources Loaded

2.5 sec

Page Rendered

825 ms

costco.co.uk screenshot

About Website

Welcome to costco.co.uk homepage info - get ready to check Costco best content for United Kingdom right away, or after learning these important things about costco.co.uk

Shop at Costco.co.uk for best deals on all products and enjoy low warehouse prices on name-brand products online and instore. Delivery included.

Visit costco.co.uk

Key Findings

We analyzed Costco.co.uk page load time and found that the first response time was 293 ms and then it took 3.4 sec to load all DOM resources and completely render a web page. This is a poor result, as 55% of websites can load faster.

Performance Metrics

costco.co.uk performance score

33

Measured Metrics

name

value

score

weighting

FCP (First Contentful Paint)

Value3.4 s

38/100

10%

LCP (Largest Contentful Paint)

Value9.3 s

1/100

25%

SI (Speed Index)

Value4.6 s

70/100

10%

TBT (Total Blocking Time)

Value590 ms

50/100

30%

CLS (Cumulative Layout Shift)

Value0.546

13/100

15%

TTI (Time to Interactive)

Value7.3 s

49/100

10%

Network Requests Diagram

costco.co.uk

293 ms

www.costco.co.uk

393 ms

cookies

174 ms

reset.css

175 ms

magiczoom.css

188 ms

Our browser made a total of 90 requests to load all elements on the main page. We found that 60% of them (54 requests) were addressed to the original Costco.co.uk, 33% (30 requests) were made to Media.costco.co.uk and 3% (3 requests) were made to Warehouses.costco.co.uk. The less responsive or slowest element that took the longest time to load (847 ms) belongs to the original domain Costco.co.uk.

Page Optimization Overview & Recommendations

Page size can be reduced by 747.1 kB (40%)

Content Size

1.9 MB

After Optimization

1.1 MB

In fact, the total size of Costco.co.uk main page is 1.9 MB. This result falls beyond the top 1M of websites and identifies a large and not optimized web page that may take ages to load. 65% of websites need less resources to load. Images take 909.4 kB which makes up the majority of the site volume.

HTML Optimization

-88%

Potential reduce by 165.2 kB

  • Original 188.3 kB
  • After minification 137.5 kB
  • After compression 23.1 kB

HTML content can be minified and compressed by a website’s server. The most efficient way is to compress content using GZIP which reduces data amount travelling through the network between server and browser. This page needs HTML code to be minified as it can gain 50.9 kB, which is 27% of the original size. It is highly recommended that content of this web page should be compressed using GZIP, as it can save up to 165.2 kB or 88% of the original size.

Image Optimization

-3%

Potential reduce by 28.8 kB

  • Original 909.4 kB
  • After minification 880.6 kB

Image size optimization can help to speed up a website loading time. The chart above shows the difference between the size before and after optimization. Costco images are well optimized though.

JavaScript Optimization

-70%

Potential reduce by 405.5 kB

  • Original 575.9 kB
  • After minification 525.7 kB
  • After compression 170.3 kB

It’s better to minify JavaScript in order to improve website performance. The diagram shows the current total size of all JavaScript files against the prospective JavaScript size after its minification and compression. It is highly recommended that all JavaScript files should be compressed and minified as it can save up to 405.5 kB or 70% of the original size.

CSS Optimization

-81%

Potential reduce by 147.5 kB

  • Original 182.2 kB
  • After minification 151.0 kB
  • After compression 34.7 kB

CSS files minification is very important to reduce a web page rendering time. The faster CSS files can load, the earlier a page can be rendered. Costco.co.uk needs all CSS files to be minified and compressed as it can save up to 147.5 kB or 81% of the original size.

Requests Breakdown

Number of requests can be reduced by 43 (49%)

Requests Now

87

After Optimization

44

The browser has sent 87 CSS, Javascripts, AJAX and image requests in order to completely render the main page of Costco. We recommend that multiple CSS and JavaScript files should be merged into one by each type, as it can help reduce assets requests from 30 to 1 for JavaScripts and from 15 to 1 for CSS and as a result speed up the page load time.

Accessibility Review

costco.co.uk accessibility score

81

Accessibility Issues

Names and labels

These are opportunities to improve the semantics of the controls in your application. This may enhance the experience for users of assistive technology, like a screen reader.

Impact

Issue

High

Buttons do not have an accessible name

High

Links do not have a discernible name

Contrast

These are opportunities to improve the legibility of your content.

Impact

Issue

High

Background and foreground colors do not have a sufficient contrast ratio.

Navigation

These are opportunities to improve keyboard navigation in your application.

Impact

Issue

High

[id] attributes on active, focusable elements are not unique

ARIA

These are opportunities to improve the usage of ARIA in your application which may enhance the experience for users of assistive technology, like a screen reader.

Impact

Issue

High

ARIA IDs are not unique

Tables and lists

These are opportunities to improve the experience of reading tabular or list data using assistive technology, like a screen reader.

Impact

Issue

High

Lists do not contain only <li> elements and script supporting elements (<script> and <template>).

Best Practices

costco.co.uk best practices score

75

Areas of Improvement

Trust and Safety

Impact

Issue

High

Does not use HTTPS

High

Includes front-end JavaScript libraries with known security vulnerabilities

Low

Ensure CSP is effective against XSS attacks

User Experience

Impact

Issue

High

Serves images with low resolution

General

Impact

Issue

Low

Detected JavaScript libraries

High

Missing source maps for large first-party JavaScript

SEO Factors

costco.co.uk SEO score

84

Search Engine Optimization Advices

Crawling and Indexing

To appear in search results, crawlers need access to your app.

Impact

Issue

High

Links are not crawlable

Content Best Practices

Format your HTML in a way that enables crawlers to better understand your app’s content.

Impact

Issue

High

Document doesn't have a valid hreflang

Mobile Friendly

Make sure your pages are mobile friendly so users don’t have to pinch or zoom in order to read the content pages. [Learn more](https://developers.google.com/search/mobile-sites/).

Impact

Issue

High

Document uses legible font sizes

High

Tap targets are not sized appropriately

Language and Encoding

  • Language Detected

    EN

  • Language Claimed

    N/A

  • Encoding

    UTF-8

Language claimed in HTML meta tag should match the language actually used on the web page. Otherwise Costco.co.uk can be misinterpreted by Google and other search engines. Our service has detected that English is used on the page, and neither this language nor any other was claimed in <html> or <meta> tags. Our system also found out that Costco.co.uk main page’s claimed encoding is utf-8. Use of this encoding format is the best practice as the main page visitors from all over the world won’t have any issues with symbol transcription.

Social Sharing Optimization

Open Graph data is detected on the main page of Costco. This is the best way to make the web page social media friendly. Here is how it looks like on Facebook: