Tools & Wizards About Us
cs50.ly screenshot

Report Summary

  • 17

    Performance

    Renders faster than
    32% of other websites

  • 100

    Accessibility

    Visual factors better than
    that of 97% of websites

  • 75

    Best Practices

    More advanced features
    available than in
    35% of websites

  • 92

    SEO

    Google-friendlier than
    74% of websites

cs50.ly

CS50: Computer Science Courses and Programs from Harvard | edX

Page Load Speed

1.8 sec in total

First Response

257 ms

Resources Loaded

1.2 sec

Page Rendered

378 ms

cs50.ly screenshot

About Website

Welcome to cs50.ly homepage info - get ready to check CS50 best content right away, or after learning these important things about cs50.ly

Introduction to Computer Science from Harvard, better known as CS50, is the largest course on the Harvard campus and more than 4,000,000 learners worldwide have registered for the course on edX.

Visit cs50.ly

Key Findings

We analyzed Cs50.ly page load time and found that the first response time was 257 ms and then it took 1.5 sec to load all DOM resources and completely render a web page. This is quite a good result, as only 30% of websites can load faster.

Performance Metrics

cs50.ly performance score

17

Measured Metrics

name

value

score

weighting

FCP (First Contentful Paint)

Value6.1 s

3/100

10%

LCP (Largest Contentful Paint)

Value6.8 s

7/100

25%

SI (Speed Index)

Value13.6 s

2/100

10%

TBT (Total Blocking Time)

Value16,390 ms

0/100

30%

CLS (Cumulative Layout Shift)

Value0.041

99/100

15%

TTI (Time to Interactive)

Value35.3 s

0/100

10%

Network Requests Diagram

cs50.ly

257 ms

cs50.ly

265 ms

cs50.harvard.edu

87 ms

cs50

321 ms

fa169e97-be64-4cc1-bad3-9534590f9a30.json

110 ms

Our browser made a total of 16 requests to load all elements on the main page. We found that 13% of them (2 requests) were addressed to the original Cs50.ly, 69% (11 requests) were made to Edx.org and 6% (1 request) were made to Cs50.harvard.edu. The less responsive or slowest element that took the longest time to load (321 ms) relates to the external source Edx.org.

Page Optimization Overview & Recommendations

Page size can be reduced by 1.8 MB (80%)

Content Size

2.3 MB

After Optimization

460.9 kB

  • HTML
  • Images
  • JavaScript
  • CSS

In fact, the total size of Cs50.ly main page is 2.3 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. 35% of websites need less resources to load. HTML takes 2.1 MB which makes up the majority of the site volume.

HTML Optimization

-86%

Potential reduce by 1.8 MB

  • Original 2.1 MB
  • After minification 2.1 MB
  • After compression 297.0 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. HTML code on this page is well minified. It is highly recommended that content of this web page should be compressed using GZIP, as it can save up to 1.8 MB or 86% of the original size.

Image Optimization

-0%

Potential reduce by 0 B

  • Original 4.7 kB
  • After minification 4.7 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. CS50 images are well optimized though.

JavaScript Optimization

-0%

Potential reduce by 0 B

  • Original 158.7 kB
  • After minification 158.7 kB
  • After compression 158.7 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. This website has mostly compressed JavaScripts.

CSS Optimization

-25%

Potential reduce by 171 B

  • Original 680 B
  • After minification 680 B
  • After compression 509 B

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. Cs50.ly needs all CSS files to be minified and compressed as it can save up to 171 B or 25% of the original size.

Requests Breakdown

Number of requests can be reduced by 3 (25%)

Requests Now

12

After Optimization

9

  • AJAX
  • Images
  • JavaScript
  • CSS

The browser has sent 12 CSS, Javascripts, AJAX and image requests in order to completely render the main page of CS50. We recommend that multiple CSS and JavaScript files should be merged into one by each type, as it can help reduce assets requests from 4 to 1 for JavaScripts and as a result speed up the page load time.

Network Requests Diagram

cs50.ly

cs50.ly

257 ms

cs50.ly

cs50.ly

265 ms

cs50.harvard.edu

cs50.harvard.edu

87 ms

cs50

cs50

321 ms

fa169e97-be64-4cc1-bad3-9534590f9a30.json

fa169e97-be64-4cc1-bad3-9534590f9a30.json

110 ms

primary-fonts.css

primary-fonts.css

69 ms

webpack-runtime-95ae3916fd93ec178110.js

webpack-runtime-95ae3916fd93ec178110.js

88 ms

framework-040df24d4f56fb3c37e1.js

framework-040df24d4f56fb3c37e1.js

125 ms

app-f4691c7b3e1eb6189e73.js

app-f4691c7b3e1eb6189e73.js

136 ms

vcd15cbe7772f49c399c6a5babf22c1241717689176015

vcd15cbe7772f49c399c6a5babf22c1241717689176015

83 ms

edx-logo-elm.svg

edx-logo-elm.svg

60 ms

0.jpg

0.jpg

71 ms

edX_by2U_white.svg

edX_by2U_white.svg

71 ms

apple-store-badge-en.svg

apple-store-badge-en.svg

86 ms

google-play-badge-en.png

google-play-badge-en.png

106 ms

async-fonts.css

async-fonts.css

29 ms

Accessibility Review

cs50.ly accessibility score

100

Accessibility Issues

Best Practices

cs50.ly best practices score

75

Areas of Improvement

Trust and Safety

Impact

Issue

High

Does not use HTTPS

Low

Ensure CSP is effective against XSS attacks

General

Impact

Issue

Low

Detected JavaScript libraries

High

Browser errors were logged to the console

High

Page has valid source maps

SEO Factors

cs50.ly SEO score

92

Search Engine Optimization Advices

Content Best Practices

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

Impact

Issue

High

Links do not have descriptive text

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

    EN

  • Encoding

    UTF-8

Language claimed in HTML meta tag should match the language actually used on the web page. Otherwise Cs50.ly can be misinterpreted by Google and other search engines. Our service has detected that English is used on the page, and it matches the claimed language. Our system also found out that Cs50.ly 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

cs50.ly

Open Graph data is detected on the main page of CS50. This is the best way to make the web page social media friendly. Here is how it looks like on Facebook: