Off by heart

Usually used in UK.
If you know something by heart, you can remember all the words in it without any help.
Learned in such a way that you can repeat it from memory.

We learned long passages of poetry off by heart.

to know anything off by heart

To learn something and keep it in mind for a longer time.

Synonyms:
To memorize
To learn by heart

Andy knows that it isn't easy for him to know anything off by heart.