Sometimes too is used with a comma, and sometimes it is not. Both can be correct. Using a comma actually depends on the intention of the writer. The comma adds an emphasis. A comma should also be used before too if there is an abrupt shift in thought. When too is used in the middle of a sentence, it interrupts the flow of the sentence, so it is usually meant to emphasize the point.
I, too, like reading.
I too like reading.
If too comes at the end of a sentence, a comma is rarely needed:
I like reading too.
There is not a hard-and-fast rule about using a comma before too, because it depends on the writer’s intent. Commas make you pause when reading, so they are used to add emphasis.
Related: We have a whole section dedicated to punctuation here, so check it out!
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