Opening books and general theory are not banned in Correspondence (online) chess. Only using chess software to analyze a position and it's lines is banned, and receiving help from another person too. (Althought this last one is, let's admit it, unverifiable)
Using computer programs is not banned if both players agree beforehand in using them.
Research during online games


Opening books and general theory are not banned in Correspondence (online) chess. Only using chess software to analyze a position and it's lines is banned, and receiving help from another person too. (Althought this last one is, let's admit it, unverifiable)
Using computer programs is not banned if both players agree beforehand in using them.
I'd like to tweak that explanation a bit. Chess Engines, and Tablebases are not allow, something like an analysis board is (that's chess software too).

site-playing-rules-a-guide-for-the-perplexed contains an overview of the rules.
(You may find this discussion a-tally-of-database-users--non-users illuminating).
What is the rule/norm about using books or google during an online game (not live, online)? Are players expected to play the entire game without any help from the bookshelf? Or is it ok to pull out the latest edition of Modern Chess Opening? What about during online tournaments?