JQ is a great tool for finding out the number of things in a JSON file.

If the top-level contents of the JSON is a list, then you can pipe it directly to the length function.

// [1, 2, {"three": 4}]
$ jq '. | length' data.json
3

It works the same for counting the number of entries (key-value pairs) in a top-level JSON object.

// { "hello": "world", "list": [1,2,3] }
$ jq '. | length' data.json
2

If you are trying to get the count of a nested value, navigate to it and then pipe that to length.

// { "hello": "world", "list": [1,2,3] }
$ jq '.list | length' data.json
3

You can even count each value in a JSON object by transforming it into an array of the values with [].

// { "hello": "world", "list": [1,2,3] }
$ jq '.[] | length' data.json
5
3

Notice, the length of "world" is 5 characters and the length of [1,2,3] is 3 elements.