when building a Telegram Bot, how do you debug it on localhost?
Run it only on localhost, kill other instances. Console log stuff.
Are you using ngrok for webhooks?
Nope, I'm using polling with Node. https://github.com/yagop/node-telegram-bot-api
Are you using a service that loops over or just a cronjob/schedule task every X seconds?
It's a websocket connection to the Telegram server and keeps the process alive, so the bot never quits running.
Create two different bots with Bot Father, the first (A) runs on localhost and the second (B) runs on my server, they scan and handle the same telegram activity. I push a new version of A with the B token on the remote instance when it's necessary.