Setup

npm install
npx office-addin-dev-certs install

Create a .ENV file with the following:

SSL_CRT_FILE=C:\Users\<username>\.office-addin-dev-certs\localhost.crt
SSL_KEY_FILE=C:\Users\<username>\.office-addin-dev-certs\localhost.key
PORT=443
HTTPS=true

Set the following registry key to sideload manifest:

[HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\WEF\Developer]
"manifest1"=<path to manifest on disk>

Start the dev server

npm start