The EBU sets out the rules for bridge played by their members in the Blue and White Books, and now for online bridge a new supplement, the Sky Blue Book.
The Blue Book is the handbook of of EBU permitted understandings, your first point of reference to find out what you can play in different events. The latest version can be viewed and downloaded here:
Section 4 covers all the rules for alerting and announcing bids to draw opponents' attention to calls that may have a special meaning. If a player is uncertain whether the regulations require an alert, but believes it would help the opponents, they should alert. The EBU summary of these rules can be found here:
The White Book contains advice for players, general regulations, regulations on scoring, advice for Tournament Directors and Appeals Committee members, and the EBU interpretations of bridge laws. The latest version can be viewed and downloaded here:
The Sky-Blue Book supplements the Blue and White Books with rules specific to online bridge. The latest version can be viewed and downloaded here:
Some members are concerned at the possibility of cheating when playing online. The EBU provides guidance to minimise the risk here:
And for matches played privately online, a document laying out general regulations can be found here: