Introduction

Transaction simulations help understand transaction effects without the need to executed it on the blockchain. Simulations provide a way to preview how a transaction interacts with smart contracts and observe changes in the blockchain state without impacting the actual network.

Why Simulations Matter?

Simulations are invaluable for testing, debugging, and ensuring that transactions perform as intended. They help identify security risks, unexpected behaviors, and potential errors before deployment, providing confidence in transaction outcomes.

Re-Simulations vs. Simulations

• Re-Simulation: Allow rerunning transactions that already exist on the blockchain. Re-simulations provide an option to modify parameters and preview different outcomes for existing transactions.
• New Simulation: Allows to create a brand-new transaction with custom parameters and preview the outcome without sending the transaction on-chain.

Walnut Simulation Form

The Walnut simulation form contains several fields used when configuring the simulation. See the following screenshot:

Here’s a breakdown of each field:

• Sender address - Use any sender address to test how the transaction behaves when initiated by another account. Private keys are not required for simulations, making simulations more flexible.
• Calldata - Calldata to be passed to the transaction. For details about the format, see Constructing Calldata.
• Block number - Block number on which the simulation will be performed. If empty, latest block number will be used.
• Chain - Chain where the transaction will be executed, such as Mainnet, Sepolia, or a custom network which is often useful in the context of appchains.
• Transaction version - For more details, refer to the official Starknet documentation.