Setting up the environment

To work with CosmWasm smart contract, you will need rust installed on your machine. If you don't have one, you can find installation instructions on the Rust website.

I assume you are working with a stable Rust channel in this book.

Additionally, you will need the Wasm rust compiler backend installed to build Wasm binaries. To install it, run:

rustup target add wasm32-unknown-unknown

Optionally if you want to try out your contracts on a testnet, you will need a wasmd binary. We would focus on testing contracts with Rust unit testing utility throughout the book, so it is not required to follow. However, seeing the product working in a real-world environment may be nice.

To install wasmd, first install the golang. Then clone the wasmd and install it:

$ git clone
$ cd ./wasmd
$ make install

Also, to be able to upload Rust Wasm Contracts into the blockchain, you will need to install docker. To minimize your contract sizes, it will be required to run CosmWasm Rust Optimizer; without that, more complex contracts might exceed a size limit.

Check contract utility

An additional helpful tool for building smart contracts is the cosmwasm-check utility. It allows you to check if the wasm binary is a proper smart contract ready to upload into the blockchain. You can install it using cargo:

$ cargo install cosmwasm-check

If the installation succeeds, you should be able to execute the utility from your command line.

$ cosmwasm-check --version
Contract checking 1.1.6

Verifying the installation

To guarantee you are ready to build your smart contracts, you need to make sure you can build examples. Checkout the sylvia repository and run the testing command in its folder:

$ git clone
$ cd ./sylvia
sylvia $ cargo test

You should see that everything in the repository gets compiled, and all tests pass.

sylvia framework contains some examples of contracts. To find them go to contracts directory. These contracts are maintained by CosmWasm creators, so contracts in there should follow good practices.

To verify the cosmwasm-check utility, first, you need to build a smart contract. Go to some contract directory, for example, contracts/cw1-whitelist, and call cargo wasm:

cw-plus $ cd contracts/cw1-whitelist
cw-plus/contracts/cw1-whitelist $ cargo wasm

wasm is an alias for wasm = "build --release --target wasm32-unknown-unknown --lib". You should be able to find your output binary in the target/wasm32-unknown-unknown/release/ of the root repo directory - not in the contract directory itself! Now you can check if contract validation passes:

sylvia $ cosmwasm-check target/wasm32-unknown-unknown/release/cw1_whitelist.wasm
Available capabilities: {"cosmwasm_1_1", "iterator", "stargate", "staking"}

target/wasm32-unknown-unknown/release/cw1_whitelist.wasm: pass

All contracts (1) passed checks!

Macro expansion

Sylvia generates a lot of code for us which is not visible in code. To see what code is generated with it go to contracts/cw1-whitelist/src/ In VSCode you can click on #[contract], do shift+p and then type: rust analyzer: Expand macro recursively. This will open a window with fully expanded macro which you can browse. This is also possible f.e. in VIM depending on your configuration. You can also use cargo expand tool from CLI for this.