Boston is a large, safe, beautiful city with lots to offer. Having that said like most cities it’s size there should be some precautions taken to avoid trouble when staying and travelling here.
This is a city where you would take normal safety precautions, a city where most crime is drug related and occurring between two familiar individuals or in crime-ridden neighborhoods. Public transportation is safe, again just practice basic safety precautions like watch out for thieves.
Boston is also safe at night, I’ve personally been to foreign countries and felt unsafe in certain areas here in Boston you will not get that. Anyplace in Boston where you would be worried of risk of your safety would be an area or neighborhood you have no business being. In Boston everything is quite simple most of the touristy areas and populated areas with business and attractions are in one general vicinity.
Overall Boston is a very safe city and you should feel safe and comfortable to enjoy yourself when here just always remember basic safety precautions and you will have an amazing trip in this beautiful coastal city.