Development TLS Certs

Development TLS certificates are only required for Office.js add-ins as they require the web server to run on https instead of http—even on localhost.

Download mkcert (pick the correct file according to your platform), rename the file to mkcert, then run the following commands from a Terminal/Command Prompt (make sure you’re in the same directory as mkcert):

./mkcert -install
./mkcert localhost 127.0.0.1 ::1

This will generate two files localhost+2.pem and localhost+2-key.pem. Move them from your current directory to the certs directory in your repo.

Note

If you are unable to use mkcert, you can alternatively use Tunneling or an online development environment such as GitHub Codespaces to run your server on https rather than http.