Spritesheet Generator is a web application that generates spritesheet JSONs.
Drag and drop your sprites image file into the application and use the tools available to draw frames. Once you're done, the output is shown in the files panel and can be copied. If you need to edit an existing spritesheet, you can drag and drop an existing spritesheet JSON file into the application along with your sprites image file.
To load icons:
npm run icons
You can also edit icons:
npm run icons -- edit