When I invited readers earlier today to ask me any question they care to about writing, editing, or English usage, this was the first to arrive: "Commas before 'too,' 'as well,' 'either,' etc. at the ends of sentences: yea or nay, and why?"
Commas often precede "as well" and "either" but may not be necessary. I would need to see a context. Periods, not commas, come at the end of sentences (well, sometimes ellipses). Using a comma before "too" is entirely discretionary; it is not necessary but can be used to place a little additional oomph on the word.
Some commas are required in formal English. Instances include preceding a coordinating conjunction when two independent clauses are joined, setting off appositives, and separating the items in a series.* Know those places.
But some commas are discretionary, used like the rests in music to mimic the slight pauses in speech. It is perfectly all right to use them thus, but be wary of going overboard. There is a tendency, much remarked upon, to indulge, knowingly or carelessly, in discretionary commas to an extent that the writer, or more properly the writer's voice, comes to resemble that of, one hesitates to point out, Henry James.
*Regarding the Oxford comma, the final comma in a series: If you are following a stylebook, use it or not as the stylebook dictates; if you are not following a stylebook, use it or not as your taste dictates; if you are arguing in public over whether or not to use it, you are annoying people with trifles.
