CDS hooks take EHR events (like when a provider opens a chart/views a patient, when an order is selected or signed, when a visit starts or ends, ...) and notify arbitrary web services that anyone can create. These services can give "card" data back to the EHR to display to the provider.
Think of the following:
To get you started, we are going to build #3, because, well, it is super interesting.
It's called "CME-ster" and it makes the following card surface in an EHR when a provider opens a chart and the patient has a history of dementia.
The link is to the awesome Curbsider's podcast which internal medicine doctors/hospitalist love
#268 Dementia Made Simple with Dr. Josh Uy
Two get CDS Hooks to work you need two things:
Somewhere you serve your code for "CME-ster"
an EHR to show these cards in
For the server part, I like repl.it, and I have some code there you can sign up for a free account and fork it at