Count elements
Their might be an easier way, but this is how I count elements in a JSON array using jq and some other command line tooling.
http https://jsonplaceholder.typicode.com/posts | jq '.[] .id' |wc -l
The above example uses httpie to fetch the JSON array, jq to extract the elements and wc to count the elements. The example data are from the JSONPlaceholder service.
If we want to count the number of comments on post with id 1 from the email: Hayden@althea.biz, we can do the following:
http https://jsonplaceholder.typicode.com/posts/1/comments | jq '.[] | select(.email == "Hayden@althea.biz") .email' | wc -l