The EBU Regulations Blue Book has been suplemented by the Sky Blue Book - this covers the addional regulations for playing online.
Full Blue Book
Alerting is also referenced in the Online Regulations
SKY BLUE BOOK – ONLINE REGULATIONS
Unlike when playing in the club, where your partner announces or alerts certain bids, on BBO, you announce and alert your own bids, using the Alert button included in the bidding box.
OPENING 1NT - When you open 1NT, you should click on alert, and type the range in the ‘explain’ box, before you complete your bid. This is visible to the opposition, but not to your partner.
OPENING @ 2 LEVEL - When you open at the two level, you click on alert, and type in one of the following – weak, strong forcing, strong non forcing, intermediate, Or describe the bid – Game Force, 8 playing tricks – unspecified suit or balanced 19-20 etc. (depending on your system – see attached table.)
STAYMAN - Stayman is alerted – and type Stayman in the explain box
RED SUIT TRANSFERS - Transfers are alerted and type either Hearts or Spades in the explain box
DOUBLE - A double that is for penalties, and not for takeout, this needs to be alerted and described as so. (Take out is asking partner to bid another suit, and therefore you are showing at least 3 cards in each of the other suits, and usually shortage in the suit bid) Take out doubles are not alertable.
Anything that could be a surprise to the opposition must be alerted – ie anything outside normal bridge assumptions.
(2 level responses, overcalling with a 4 card suit, doubles for penalties to name a few)
DO NOT type explanations in CHAT. – as this is visible to your partner. - type in the 'box'
According to the Sky Blue Book, this is required even if your profile is completed.
You cannot Over Alert on BBO, as you are not giving information to your partner, only the opposition - it would be good etiquette to alert ALL bids with a potential unexpected meaning. Alert all the way to 7NT! Saves time later, answering questions to the table.
If you feel you have been damaged by a failure to alert, or incorrect alert then please call the TD. (unless it’s a casual game without a TD )
FORGET TO ALERT? - If you forget to alert / announce – you can click on your own bid, and add it immediately.
If you think someone should have alerted / announced but hasn’t, you can click on their bid – they are then required to complete the explain box – and not write anything in chat.
General questions about general bidding methods and carding agreements can be addressed to all at the table so that either opponent can answer, and all can see the answers.
Specific questions about particular calls should be via the alert/announcement mechanism (in which case both members of the opposing pair will see any revised explanation), or through private message to the opponent making the bid.