WebAssembly (WASM) is a binary instruction format that lets code written in languages like Rust, C++, and Go run in web browsers and blockchain virtual machines at near-native speed. In blockchain, WASM serves as an alternative execution environment to the Ethereum Virtual Machine, enabling faster and more flexible smart contract execution.
Smart contracts need a runtime, a virtual machine that reads the contract's bytecode and executes it. Ethereum uses the EVM (Ethereum Virtual Machine), which was purpose-built for blockchain in 2015. WASM is a general-purpose bytecode format originally designed for web browsers by the World Wide Web Consortium.
Blockchain teams adopted WASM because it solves real limitations of the EVM. WASM executes faster, supports more programming languages, and benefits from a large existing toolchain built by the broader software industry. You can write a WASM smart contract in Rust, compile it, and deploy it to a compatible chain without learning a domain-specific language like Solidity.
Several major blockchains chose WASM as their primary or secondary execution environment.
If you already write Rust or C++, you can build WASM-compatible smart contracts without learning a new language. This significantly lowers the barrier to entry for experienced software engineers moving into blockchain development.
WASM also supports memory-safe execution and formal verification more naturally than the EVM, which matters for high-stakes financial contracts. Projects building on Substrate or CosmWasm can write contract logic with the same safety guarantees as systems software, then compile directly to the runtime format the chain expects.
https://webassembly.org
https://docs.substrate.io/reference/wasm-runtime
https://cosmwasm.com
https://near.org/developers