This is a very lightly tweaked version of https://github.com/swagger-api/swagger-editor for our use case.
Visit https://catalystdevelopment.github.io/
Or, if developing locally, simply open index.html in your web browser
Modify the swagger.json file. You may wish to use http://editor.swagger.io/ to preview how your changes will look (Import as yaml - easier to modify - then export as JSON)
npm i (Only the first time)
npm run-script build