To solve your issue you need support by some kind of scripting plugin, for example NppExec plugin and its companion NppEventExec.
Install NppExec and NppEventExec plugins using Plugins Admin. After Notepad++ has been restarted navigate to (menu) Plugins -> NppExec -> Execute NppExec Script In the dialog popping up enter the following script: npp_console keep npp_menucommand Path/To your JSON formatting plugin's/menu entryIf your are using for example JSTool plugin to format your JSON files, line 2 of the script above has to be npp_menucommand Plugins/JSTool/JSFormat. In case you are using JsonTools plugin, line 2 of the script above has to be npp_menucommand Plugins/JsonTools/Pretty-print current JSON file. Please note: The menu entry’s path is case sensitive and has to be localized. That means, if the Plugins menu has another name in your Notepad++ UI language, you need to adapt the command accordingly.
Click button Save. In the small dialog popping up enter AutoFormatJson as name for the script. Click button Save to close the saving dialog. Click button Cancel to close the script editing dialog. Navigate to (menu) Plugins -> NppEventExec -> Edit rules In the toolbar at the left, click button Add a new rule (mouse-hover over the buttons to get their tooltip texts). In the toolbar at the left, click button Edit the selected rule. Create a new rule by entering the following data into the dialog popping up (Please note: The edit field NppExec command has to contain the name of the NppExec script you saved in step 5. Edit field Regex has to contain the following: (?i).*\.json):a0ef2c92-f43c-4f8c-8777-243f69d2e55d-grafik.png
Click button Apply to close the rule editing dialog. In plugin’s main dialog click button Save to save your changes. Click button Close to close plugin’s main dialog.Now you can load a JSON file and it should be pretty-printed automatically.