JSON is js object, so we can use javascript syntax highlighting. First, Setting > Style Configure and then select Javascript in list box. you will see User ext in below. Fille json and then Save & Close. Second, Setting > Preference and Go to File Association Tab > Customize and type .json in textbox and click -> . You will see .json in Registered exts: listbox. After that , you can double click to .json file. It's will open with notepad++ and also include syntax highlighting. If you don't like syntax, you can change javascript syntax highlighting in Setting > Style Configuration > Javascript.