All three - also, too and as well - are pretty interchangeable. They all mean "in addition". The difference is in where they come in a sentence, as you already seem to know by the examples you used.
"too" and "as well" like to come at the end of a sentence.
e.g. ...Tim is here too. / ...Tim is here as well.
BEWARE! Sometimes changing the position can change the meaning:
e.g. She speaks it too. / She, too, speaks it.
The first sentence can mean anything from "she speaks it in addition to speaking something else", to "she speaks it in addition to someone else" or "she speaks it in addition to doing something else with it".
The top one isn't used, as "also" doesn't normally come at the end of a sentence. The second one isambiguous, as with the first sentence in my other example. The bottom one would mean the sa