Compile a Rust smart contract module#

This guide will show you how to compile smart contract module written in Rust to a Wasm module.


Make sure to have Rust and Cargo installed and the wasm32-unknown-unknown target, together with cargo-concordium and the Rust source code for a smart contract module, you wish to compile.

See also

For instructions on how to install the developer tools see Install tools for development.

Compiling to Wasm#

To help building smart contract modules and to take advantage of features such as contract schemas, Concordium recommends using the cargo-concordium tool for building Rust smart contracts.

In order to build a smart contract, run:

$cargo concordium build

This uses Cargo for building, but runs further optimizations on the result.


If you receive an error similiar to the one below, you need to update your cargo-concordium to version 3.0 or later.

Error: Could not build smart contract.

Caused by:
   0: Could not build module schema.
   1: Could not generate module schema from Wasm module.
   2: Unsupported instruction 0xc0

If you want a smaller code footprint, enable the wee_alloc feature by using:

$cargo concordium build --features wee_alloc

See also

For building the schema for a smart contract module, some further preparation is required.


It is also possible to compile using Cargo directly by running:

$cargo build --target=wasm32-unknown-unknown [--release]

Note that even with --release set, the produced Wasm module includes debug information.

Running the cargo concordium build command will produce a smart contract module which can be found relative to your project root folder in ./target/concordium/wasm32-unknown-unknown/release/my_module.wasm.v1. Alternatively, you can supply the location where to store the smart contract module using the --out option. For example running the following command will output your smart contract module into the root folder of your project in a file name my_module.wasm.v1.

$cargo concordium build --out ./my_module.wasm.v1


cargo-concordium produces several smart contract modules with different suffixes. The suffix corresponds to the smart contract version, i.e. my_module.wasm/my_module.wasm.v0 for V0 contracts and my_module.wasm.v1 for V1 contracts. Concordium recommends using the wasm module with the .v1 extension (the most-up-to date smart contract version). The file my_module.wasm.v1 will be used when deploying a smart contract on-chain.