I'd like to know the most cost-effective way to monitor changes to the value of an attribute returned by a URL in JSON format. That is, I have the URL of an API that returns something like:
{"high": 340.0, "volume": 261.83}
And I would like to create a service to call this URL from time to time and notify me if the value of the "high" attribute meets a condition, is greater or less than an x value, for example. It can be in any language. Has anyone ever created anything like this?