1 in a suit = 4 cards and 12-20 HCP;Bidding System
The bidding is mostly natural with no convention bids, not even Stayman or Blackwood. The idea is that the bidder never asks but rather describes his hand. The exceptions to natural bidding are: stopper-seeking bids below 3NT, control-showing cuebids and splinters. These and more are described below.
Openings:
1 in a suit = 4 cards and 12-20 HCP;
1NT = 15-18 HCP, 2NT = 21 - 23 HCP, balanced hand with no 5 card suits;
2 in a suit = 5 cards and 21+ HCP.
Level 3+ openings are not considered as there's no opponents' interference.
Responses and the subsequent bidding follow common sense. New suit is usually forcing, nearest NT is weak, raise 1 level is inviting, jump shift is game forcing, jump raise to non-game is forcing slam invite if the bidder's hand is not limited yet, e.g. 1
- 3 is forcing slam invite, and 1
- 3 too, while 1 - 2NT and 1 - 2NT are inviting game with 4 cards support in the opener's suit.
Responses 1 over 1 require 5+ HCP; 2 over 1 require 10+ HCP from the responder or 15+ HCP for opener's rebid; new suit at level 3 is game forcing and requires 24+ HCP total. Suit openings at level 2 are one-round forcing; responses 2 over 2 are natural and forcing although may be done with 0 HCP, e.g. 2 - 2 = 0+ HCP, 4+ cards , forcing. Generally, calculate the total balance and move on accordingly.
After NT opening major responses invite game with 5 cards in the suit (no transfer bids). This is the only situation when new suit is non-forcing. It's OK to bid a 3 card minor for a 1 round forcing (this is an alternative to Stayman). Generally, with strong hand it is safe to "cheat" suit length if the partner's previous bidding shows that he cannot fully support this suit, e.g. 1 (= 12-20 HCP, 4+ cards ) - 1 (= 5+ HCP, 4+ cards , <=4 cards 
) | 1NT (= 12-14 HCP, <=3 cards ) - 2 = 11+ HCP, 5+ cards , may not have 4 cards . As a consequence, it is not recommended to raise the partner's 4 card suit with 3 card support.
With major trump new suit lower than 3 in the trump is semi-natural, i.e. shows honors and invites game, e.g. 1 - 2 | 3
= opener's hand is not minimum and need support, like KJx. This artificial bid may turn later into a cuebid that invites slam, e.g. 1 - 1 | 2 - 3 (= game invite with honors or cuebid) | 3 (= opener suggests to stop, no honor) - 4 = responder is very strong with cuebids in and , i.e. ace of and ace or king of . Reverse order of "hidden cuebids" shows that there's a king (not an ace) in the initially skipped suit, e.g. 1 - 1 | 2 - 3 | 3 - 4 = ace of and king of .
With minor trump at level 2 and 3 new suit is not natural and shows absence of NT stopper, e.g. 1 (= 12-20 HCP, <=4 cards in majors) - 2 (= 10-11 HCP, <= 3 cards in majors) | 2 = 14-20 HCP, no stopper in (assumes stopper in because 2 skipped). This artificial bid may also turn later into a cuebid for slam.
Slam bidding is based on cuebids, splinters and "descriptive" 4/5NT (there's no Blackwood or Gerber). When game is forced, any non-trump suit is a slam cuebid, e.g. 1 - 3 (= slam invite) | 2 = cuebid (a control: ace, king, single or void). Requirements for cuebid: sufficient strength, a control in the suit and normally 2 "slam aces" which include aces and honors in trump suit (king, queen) - 6 total. Number of "slam aces" required for the first cuebid varies depending on the previously shown strength of the bidder, e.g. after 2 level opening 3 "slam aces" are required, while the responder may have only 1.
Unusual jump to a new suit is a splinter bid that shows a single or void in this suit and good fit in the most likely trump, e.g. 1 - 3 = splinter with single or void and trump (2 is sufficient to force game with 6+ cards ); another example: 1 - 2 | 4 = splinter with single or void and trump (3 is sufficient to force game with 4+ cards , longer suit may be shown by bidding 4 in the next round); less obvious example: 1NT - 3 (= 9+ HCP, 5+ cards ) | 3NT - 5 = splinter with single or void and trump.
4NT normally shows slam controls in all suits and 3+ "slam aces". The number of "slam aces" that is shown with 4NT varies depending on the previously shown strength of the bidder. After 2 level opening 4 "slam aces" are required, while the responder may have only 2, e.g. 2 - 4 (= splinter, single or void ) | 4 (= cuebid, control in H) - 4NT = control in (not shown earlier), 2+ "slam aces". Important information is derived when 4NT is skipped which means that either a control in some suit is missing or number of "slam aces" is insufficient.
Variations of bridge bidding are virtually endless and cannot be documented in full. The program "understands" this and at any moment can explain you what was shown currently and what is the meaning of any next bid. To obtain current information press F1. To find out what your next bid will mean press F2 and then bid.
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