Announcing is the bridge term used for complying with a duty to give a (very short) description of what partner's bid actually means.

Three Golden Rules of Announcing

1. Never announce your own bids
2. Once the auction becomes competitive NO bids are ever announced
3. A player's second (or subsequent) bid is never announced

Rules for each type of bid

1♣  and 1♦ openings

'Prepared or short 1♣  and 1♦ openings (which are non-forcing but may be made on 2 or fewer cards in the suit) are announce by 'May Be' followed by the minimum number e.g. 'May be 2'. NB you don't say 'Could be short'.

If the hand could have another 5 card suit in the context of a balanced hand then the announcement must include such details e.g. for 1♣  'May be 2 with a 5-card Diamond Suit'

Other conventional 1♣  or 1♦ calls e.g. precision, Canape or two-way openings such as a Polish Club, or any opening which may be short but is unconditionally forcing must be alerted.

Opening 1NT and Responses

As per the Golden Rules - this does NOT include 1NT rebids or overcalls.

State the Range e.g. '12-15'. Where the opening could have singleton follow this by 'May contain a singleton' (although the rules do not say, if the singleton could only be in a certain suit then include the suit.) e.g. '12-15, may contain a singleton ♥ '

Stayman 2♣ : Is announced  as 'Stayman' even if it does not promise a 4-card major - provided there has been no intervention and is asking for a four-card major. Do NOT alert the 2♦ standard response. Alert any response of 2NT or higher or 2♠ where it does not deny 4 hearts.

Red Suit Transfers (2♦ =♥ and 2♥ =♠ ): are announced by stating the denomination shown. The bid must show 5(+) cards in the major and again, is only after a 1NT opening with no interference

Two of a Suit Openings

Only Natural (5+ card) openings are announced. They are announced by using one (or more) of the 4 phrases below: -

• "Strong, forcing"
• "Strong, not forcing"
• "Intermediate"
• "Weak"

A hand may come into more than one category: An example given in the Blue Book is "6-12 opening would be described as 'weak to intermediate'"

A two bid that may (but may not have) a secondary suit is regarded as natural. A two-bid that definitely has a secondary suit (e.g. Lucas) has to be alerted.

All two-level suit openings that are not announced must be alerted.

Please read the guidelines of what is a 'strong' hand.

2NT openings and responses

Natural 2NT openings are announced by stating the range e.g. by saying "20-22" : Unlike 1NT openings it is not necessary to say, if appropriate' 'May contain a singleton'

Stayman 3♣: is announced only if there has been no intervention (X) and only if it asks for 4-card majors. Puppet / 5-card Stayman must be alerted. The response of 3♦ is not alerted. Alert any response of 3NT or higher or where 3♠ does NOT deny 4 hearts

Red Suit Transfers (3♦ =♥ and 3♥ =♠ ): are announced by stating the denomination shown. The bid must show 5(+) cards in the major and again, is only after a 2NT opening with no interference

Common Errors

1. Announcing a transfer to Clubs or Diamonds e.g. 1N : 2♠
2. Alerting the response of 2♦ after a Stayman enquiry
3. Alerting the completion of the transfer if there are no possible alternative calls that can be made e.g. super-accepts
4. Announcing in a competitive auction e.g after 1NT has been doubled.

Summary

Announcing was introduced to try and a) speed up the game b) reduce the amount of UI that could be provided by asking about the range of a 1NT call or the meaning of the alert of a transfer.

There are actually very few situations (in number) where announcing is correct - but they are very common  and simple ones.

If a call is announced when it should not be then the players may be in receipt of unauthorised information. In theory a director could award a procedural penalty - but this is most likely to just be a warning/ explanation of the rules.