Monitoring Web Page Contents

I need to develop a web application which should monitor another website pages. (i.e) To check whether the contents are getting updated timely or not. For example some contents needs to be updated every 5 minute, some needs to be updated every 1 hour, etc.,

My current idea is to download the required pages using wget and generate a complete json file in the backend. Then my application will download the json via ajax call and based on that I will do some alerting.

My question is, Is this the right way? Or any other better approaches already there to acheive this.