What Are Simulations?
BridgeDummy's simulation engine lets you test bridge decisions before you commit to them at the table. Instead of guessing whether 3NT or 4 Spades is the better contract, you can run thousands of random deals that match your hand and constraints, then see which option performs best.
The engine uses a Monte Carlo approach: it generates a large number of deals that fit the hand shapes and point ranges you describe, then analyzes every one of them with a double-dummy solver. The result is a clear statistical picture of how each contract or lead performs across realistic scenarios.
Setting Up Your Hand
Start by selecting your 13 cards. Click the card grid to toggle cards in each suit. You must select exactly 13 cards before you can run a simulation. If you know some of your partner's cards, you can enter those too.
Your hand is always in the South seat. Once your cards are locked in, the engine knows which cards remain available for the other three seats and will only generate deals using the remaining 39 (or fewer, if you also specified partner cards).
Defining Opponent Constraints
This is where the real power lives. For each of the other three seats (partner, left-hand opponent, right-hand opponent), you can set constraints like HCP range, minimum or maximum suit lengths, whether the hand is balanced, and whether it contains a good suit.
You can also add multiple alternative constraint sets for a single seat, connected by OR logic. For example, you might say partner has either 12-14 HCP balanced, or 15-17 HCP with five or more hearts. The engine will generate deals that satisfy at least one of those alternatives.
Keep your constraints realistic. If you make them too tight, the engine may struggle to generate enough valid deals and you will see a low-sample warning in your results.
Choosing a Simulation Type
BridgeDummy supports two simulation modes: bidding and lead. In bidding mode, you add one or more contracts you want to compare. The engine scores each one across all generated deals, showing average score, making percentage, and matchpoint or IMP results.
In lead mode, you pick a single contract and declarer. The engine evaluates every possible opening lead from your hand, ranking them by average tricks and defeat rate. This is perfect for those moments when you are staring at your hand and wondering which card to put on the table.
Reading Your Results
After the simulation finishes, you will see ranked tables. For bidding simulations, contracts are sorted by average score, making percentage, and average IMPs or matchpoints. The top three options are highlighted so you can spot the winners quickly.
For lead simulations, each possible lead card is ranked by average tricks (lower is better for defense) and defeat rate (higher is better). Look for cards that consistently beat the contract across many different layouts.
If any contract in your bidding simulation uses conditional rules, hover over it to see how often each condition triggered and which final contract was reached. This helps you understand the full picture behind competitive or complex auction decisions.
Saving and Loading Sessions
You can save up to 30 simulation setups. After running a simulation, click the Save button to store your hand, constraints, contracts, and results. Each saved session is labeled with your hand shape for easy identification.
To revisit a previous session, open the Saved Simulations panel and click any entry. Your entire setup loads back in, including all constraints and results, so you can adjust a single variable and re-run without rebuilding from scratch. This is great for iterative analysis where you want to see how one small change affects the outcome.
Saved sessions live in your account, so you can sign in on another device and load them from the Saved Simulations panel.