Compiling Contracts

To compile all of the contract sources within the contracts/ subfolder of a project:

$ brownie compile

Each time the compiler runs, Brownie compares hashes of each contract source against hashes of the existing compiled versions. If a contract has not changed it is not recompiled. If you wish to force a recompile of the entire project, use brownie compile --all.

If one or more contracts are unable to compile, Brownie raises an exception with information about why the compilation failed. You cannot use Brownie with a project as long as compilation is failing. You can temporarily exclude a file or folder from compilation by adding an underscore (_) to the start of the name.

Supported Languages

Brownie supports Solidity (>=0.4.22) and Vyper (0.1.0-b16). The file extension determines which compiler is used:

  • Solidity: .sol
  • Vyper: .vy


Project contracts can import interfaces from the interfaces/ subfolder. Interfaces are not considered primary components of a project. Adding or modifying an interface only triggers a recompile if a contract is dependent upon that interface.

The interfaces/ folder is of particular use in the following situations:

  1. When using Vyper, where interfaces are not necessarily compilable source code and so cannot be included in the contracts/ folder.
  2. When using Solidity and Vyper in the same project, or multiple versions of Solidity, where compatibility issues prevent contracts from directly referencing one another.

Interfaces may be written in Solidity (.sol) or Vyper (.vy). Vyper contracts are also able to directly import JSON encoded ABI (.json) files.

Compiler Settings

Settings for the compiler are found in brownie-config.yaml:

evm_version: null
minify_source: false
    version: 0.6.0
    optimize: true
    runs: 200

Modifying any compiler settings will result in a full recompile of the project.

Setting the Compiler Version


Brownie supports Solidity versions >=0.4.22 and Vyper version 0.1.0-b16.

If a compiler version is set in the configuration file, all contracts in the project are compiled using that version. It is installed automatically if not already present. The version should be given as a string in the format 0.x.x.

If the version is set to null, Brownie looks at the version pragma of each contract and uses the latest matching compiler version that has been installed. If no matching version is found, the most recent release is installed.

Setting the version via pragma allows you to use multiple versions in a single project. When doing so, you may encounter compiler errors when a contract imports another contract that is meant to compile on a higher version. A good practice in this situation is to import interfaces rather than actual contracts, and set all interface pragmas as >=0.4.22.

The EVM Version

By default evm_version is set to null. Brownie sets the ruleset based on the compiler:

  • byzantium: Solidity <=0.5.4
  • petersburg: Solidity >=0.5.5 <=0.5.12
  • istanbul: Solidity >=0.5.13, Vyper

You can also set the EVM version manually. Valid options are byzantium, constantinople, petersburg and istanbul. You can also use the Ethereum Classic rulesets atlantis and agharta, which are converted to their Ethereum equivalents prior to being passed to the compiler.

See the Solidity EVM documentation or Vyper EVM documentation for more info on the different EVM versions and how they affect compilation.

Compiler Optimization

Compiler optimization is enabled by default. Coverage evaluation was designed using optimized contracts, there is no need to disable it during testing.

See the Solidity documentation for more info on the solc optimizer.

Source Minification

If minify_source is true, the contract source is minified before compiling. Each time Brownie is loaded it will then minify the current source code before checking the hashes to determine if a recompile is necessary. This allows you to modify code formatting and comments without triggering a recompile, at the cost of increased load times from recalculating source offsets.

Installing the Compiler

If you wish to manually install a different version of solc:

>>> from brownie.project.compiler import install_solc
>>> install_solc("0.5.10")