The AWS Utility allows you to make queries against the Amazon Web Services API. For the simplest usage, enter any UPC code and click submit. You will see the XML appear in the text field below and some basic information about the item.
If you would like to see that result parsed as JSON, then change the responseType. Changing the ResponseGroup alters the content that is returned by Amazon. Almost every ResponseGroup is support by the XML system, but only about 1/3 are supported by the JSON parser (mostly because of parser limitations). The Operation is the what you would like AWS to do, if you use ItemLookup or SimilarityLookup then the UPC field will expect a UPC code. If you use ItemSearch, then the UPC field is actually a keyword search.