You have to use the plugin manager of Notepad++ and search for the JSON plugin. There you can easily install it.

This answer explains it pretty good: How to reformat JSON in Notepad++?

Answer from Kiril on Stack Overflow
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GitHub
github.com › sunjw › jstoolnpp
GitHub - sunjw/jstoolnpp: A JavaScript (JSON) tool for Notepad++ (formerly JSMinNpp) and Visual Studio Code. · GitHub
JSON tree viewer. Install "JSTool" from Plugin Manager in Notepad++. Or download it from http://sourceforge.net/projects/jsminnpp/ and copy JSMinNpp.dll to plugin directory of Notepad++.
Starred by 306 users
Forked by 28 users
Languages   JavaScript 98.8% | C++ 0.7% | C 0.3% | PHP 0.1% | Python 0.1% | CSS 0.0%
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Sunjw
sunjw.us › jstool › npp
JSTool - A JavaScript tool for Notepad++
For Notepad++ 7.6 to 7.6.2: please update to Notepad++ 7.6.3. Run Notepad++, you will see JSTool in "Plugins" menu. ... Run Notepad++. Open menu: "Plugins" - "Plugin Manager" - "Show Plugin Manager". Under "Installed" tab, select "JSTool".
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Notepad++ Community
community.notepad-plus-plus.org › topic › 22151 › i-can-t-install-the-jstool-plugin-how-can-i-figure-it
I can't install the JSTool plugin,How can i figure it | Notepad++ Community
November 17, 2021 - So maybe you just need to try again. Also, your download box says plugin version 1.2001.1, but when I downloaded from NPP 8.1.9.1, it downloaded plugin version 1.2107.2 … I don’t know if maybe the developer of that plugin got rid of the old version when they released the new version… but maybe it’s not downloading the old version correctly. If so, maybe you could download the newest zipfile directly and unzip the JSMinNPP.dll into c:\program files\Notepad++\Plugins\JSMinNPP\JSMinNPP.dll and restart Notepad++ yourself.
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SourceForge
sourceforge.net › projects › jsminnpp
JSToolNpp download | SourceForge.net
Download JSToolNpp for free. A JavaScript tool for Notepad++ and Visual Studio Code. A JavaScript (JSON) tool for Notepad++ (formerly JSMinNpp) and Visual Studio Code. * Douglas Crockford's JSMin algorithm to minimize JavaScript code.
Rating: 4.9 ​ - ​ 14 votes
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Techtown
atechtown.com › home › text editors › jstool plugin for notepad++ – features, download, how to install and use
JSTool Plugin for Notepad++ – Features, Download, How to Install and Use - Techtown
December 28, 2022 - Open Notepad++ and Go to Plugins–>Plugins Admin. Search and select the JSTool plugin and click the install button to install the plugin in Notepad++.
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SourceForge
jsminnpp.sourceforge.net
JSTool - A JavaScript tool for Visual Studio Code
Really helpful to JavaScript coder on Visual Studio Code. Easy to use it. Made in China. ... JavaScript minify. JavaScript/JSON format. Sort JSON data alphabetically. JSON tree viewer. ... Minor tweak. ... Run Visual Studio Code. Open "Extensions" from Activity Bar. Search "jstool". Click "Install" ...
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SourceForge
sourceforge.net › home › open source software › software development › code generators › jstoolnpp › files
JSToolNpp - Browse Files at SourceForge.net
Project site: http://www.sunjw.us/jstool · JavaScript minify. JavaScript/JSON format. Sort JSON data alphabetically. JSON tree viewer. Install "JSTool" from Plugin Manager in Notepad++. Or download it from http://sourceforge.net/projects/jsminnpp/ and copy JSMinNpp.dll to plugin directory ...
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GitHub
github.com › notepad-plus-plus › notepad-plus-plus › issues › 5145
JSTool plugin can't be installed · Issue #5145 · notepad-plus-plus/notepad-plus-plus
September 9, 2018 - You signed out in another tab or window. Reload to refresh your session. You switched accounts on another tab or window. Reload to refresh your session. ... Click Install. Notepad says it "Will be restarted". Click Yes. Notepad++ is closed · Notepad++ is started; the JSTool plugin is present
Author   hinst
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Softpedia
softpedia.com › windows › office tools › text editors › jstoolnpp
JSToolNpp - Download - Softpedia
The tool is suitable for managing even large files, over 10 MB in size. Installing the tool is simple since all you need to do is copy the dynamic link library in the designated folder in the Notepad++ install directory.
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Notepad++ Community
community.notepad-plus-plus.org › topic › 11978 › jstool-plugin-will-not-install
JSTool Plugin will not install | Notepad++ Community
June 27, 2016 - When I go to: https://sourceforge.net/projects/jsminnpp/files/Uni/ I see several files, and “JSToolNPP.1.16.10.uni.zip” downloads fine. And it contains “JSMinNPP.dll”. I copied the dll into NPP’s plugin directory and re-running NPP shows it in the Plugins menu and it works.
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SourceForge
sourceforge.net › home › open source software › software development › code generators › jstoolnpp › files
JSToolNpp - Browse /Vsc at SourceForge.net
Project site: http://www.sunjw.us/jstool · JavaScript minify. JavaScript/JSON format. Sort JSON data alphabetically. JSON tree viewer. Install "JSTool" from Plugin Manager in Notepad++. Or download it from http://sourceforge.net/projects/jsminnpp/ and copy JSMinNpp.dll to plugin directory ...
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GitHub
github.com › SkyN9ne › JSToolNpp
GitHub - SkyN9ne/JSToolNpp: A tool / plugin for Notepad++ and Visual Studio Code adding features for JavaScript and JSON. Formerly called JSMinNpp · GitHub
Install JSTool from the Plugin Manager in Notepad++. Or alternatively download it from from GitHuB or https://sourceforge.net/projects/jsminnpp/ and copy JSMinNpp.dll to the plugin directory of Notepad++ (By default on Windows it's typically ...
Author   SkyN9ne
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SourceForge
sourceforge.net › home › open source software › software development › code generators › jstoolnpp › files
JSToolNpp - Browse /Src at SourceForge.net
Project site: http://www.sunjw.us/jstool · JavaScript minify. JavaScript/JSON format. Sort JSON data alphabetically. JSON tree viewer. Install "JSTool" from Plugin Manager in Notepad++. Or download it from http://sourceforge.net/projects/jsminnpp/ and copy JSMinNpp.dll to plugin directory ...
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GitHub
github.com › sunjw › jstoolnpp › blob › master › README.md
jstoolnpp/README.md at master · sunjw/jstoolnpp
JSON tree viewer. Install "JSTool" from Plugin Manager in Notepad++. Or download it from http://sourceforge.net/projects/jsminnpp/ and copy JSMinNpp.dll to plugin directory of Notepad++.
Author   sunjw
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SourceForge
sourceforge.net › home › open source software › software development › code generators › jstoolnpp › files
JSToolNpp - Browse /Uni at SourceForge.net
Project site: http://www.sunjw.us/jstool · JavaScript minify. JavaScript/JSON format. Sort JSON data alphabetically. JSON tree viewer. Install "JSTool" from Plugin Manager in Notepad++. Or download it from http://sourceforge.net/projects/jsminnpp/ and copy JSMinNpp.dll to plugin directory ...