How to tell if a website is using a CDN

You can tell if a website is using a CDN by using the following two websites

1. https://uutool.cn/cdn-check/
2. https://www.cdnplanet.com/tools/cdnfinder

Based on https://apsgo.pcoic.com/这个域名为例

You can see that this domain uses a CDN, and it's a CDN from Aliyun