How may I use the GraphQL Playground for local development? I installed the desktop app. When I enter "http://localhost:8080" as the URL endpoint, there's an error "Server cannot be reached." My curl requests succeed.

there should be a line in your package.json that starts everything up including start playground, mine looks like this

"dev": "npm-run-all --parallel start playground"

Try

<http://localhost:8080/playground>