Extensible Markup Language (XML) is a markup language that is both human-readable and machine-readable.
To work with XML data format there are professional vendor tools such as XML Spy and oXygen, that allow manipulating, formatting, and correcting XML. Most modern browsers also have plugins to properly format XML for easier readability. Free browser plugins for Chrome can be found in the Chrome Web Store.
Rich Site Summary (RSS) is a format for news-related sites, weblogs and other online publishers feed formats.
RSS data format is XML based, same tools and plugins can be used for viewing and manipulating it as XML. Additional background and information about RSS can be found within Wikipedia RSS Article.
Working with JSON data format is not always intuitive. In most cases the data is compressed. All new line, spaces, and line breaks are removed. Most modern browsers also have plugins to properly format JSON that will allow for easier readability. Free browser plugins for Chrome can be found in the Chrome Web Store. Likewise, there are several online JSON formatters that allow pasting or adding JSON to the URL.