Try XML Tools. Plugins -> XML Tools -> Pretty Print (libXML) or (XML only - with line breaks Ctrl + Alt + Shift + B)

You may need to install XML Tools using your plugin manager in order to get this option in your menu.

In my experience, libXML gives nice output but only if the file is 100% correctly formed.

Use JSTool

As of Notepad++ v7.6, you can use the Plugin Admin option in Notepad++ to install JSTool.

Manual Install

1. Download it from https://www.sunjw.us/jstool/npp/#download
2. Copy JSMinNpp.dll to the plugin directory of Notepad++. You may need to create a directory named "JSMinNPP" in the plugin directory after version 7.6.3

Here's an example of JSON that's been formatted using the tool:

{
  "menu" : {
    "id" : "file",
    "value" : "File",
    "popup" : {
      "menuitem" : [{
      "value" : "New",
          "onclick" : "CreateNewDoc()"
        }, {
          "value" : "Open",
          "onclick" : "OpenDoc()"
        }, {
          "value" : "Close",
          "onclick" : "CloseDoc()"
        }
      ]
    }
  }
}

Tip: Select the code you want to reformat, then Plugins | JSTool | JSFormat.

You need to install JSON Viewer plugin in NotePad++. plugins > plugin Manager > JSON Viewer > Install. After plugin install select text you want to format and click on plugins > JSON Viewer > Format JSON.

Checkout latest version of Notepad++ to get all updated and latest plugins.

TextFX has the options to insert line breaks and tabbing:

Since I upgraded to 6.3.2, I use XML Tools.

• install XML Tools via the Plugin Admin (Plugins → Plugins Admin... Then search for "XML Tools", check its box and click the "Install" button).
• use the shortcut Ctrl+Alt+Shift+B (or menu → Plugins → XML Tools → Pretty Print)

In older versions: menu → TextFX → HTML Tidy → Tidy: Reindent XML.