In an organization running O365, every once in a while you’ll need to jump through hoops inside O365 or Powershell to find your tenant ID. While it’s not that terrible, it’s certainly not speedy. If you’re a Microsoft Partner, you often need the Tenant ID for various Microsoft paperwork. It can be a hassle to collect this from your customer, or get credentials setup early enough in the engagement process with them. For you, this is a lifesaver!
The brilliant folks at ShareGate came up with http://www.whatismytenantid.com. Enter any domain name associated with your tenant – including the .onmicrosoft.com:
and a few nanoseconds later:
Note that if your browser window is smallish, you may get an add that covers the ID and Copy to clipboard button, so hit maximize.