Catalyst is a tool for compiling and debugging ThunderChain smart contracts. Developers may work with it online to compile, deploy and execute contracts in a test environment that simulates the real world of ThunderChain. By doing so, bugs can be detected before the contracts are launched. Catalyst supports both EVM and WASM virtual machines, facilitating developers to code with Solidity or C/C++ languages, etc.. It also provides multiple contract templates for developers' reference.