https://tldrlegal.com/license/pokemon-go-terms-of-service-
"Conduct, General Prohibitions, and Niantic’s Enforcement Rights
You agree that you are responsible for your own conduct and User Content while using the Services, and for any consequences thereof. Please refer to our Trainer Guidelines (https://pokemongo.nianticlabs.com/support/guidelines/en) for information about the kinds of conduct and User Content that are prohibited while using the Services. By way of example, and not as a limitation, you agree that when using the Services and Content, you will not:
[...]"
That link redirects to https://support.pokemongo.nianticlabs.com/hc/en-us/articles/221993967
"No cheating.
Don’t do it. Play fair. Pokémon GO is meant to be played on a mobile device and get you outside to explore your world! Methods of cheating, unfortunately, are limited only by cheaters’ imaginations, but include at a minimum the following: using modified or unofficial software; playing with multiple accounts (one account per player, please); sharing accounts; using tools or techniques to alter or falsify your location; or selling/trading accounts."