forge build


forge-build - Build the project’s smart contracts.


forge build or forge b [options]


Build the project’s smart contracts.

The command will try to detect the latest version that can compile your project by looking at the version requirements of all your contracts and dependencies.

You can override this behaviour by passing --no-auto-detect. Alternatively, you can pass --use <SOLC_VERSION>.

If the command detects that the Solidity compiler version it is using to build is not installed, it will download it and install it in ~/.svm. You can disable this behavior by passing --offline.

The build is incremental, and the build cache is saved in cache/ in the project root by default. If you want to clear the cache, pass --force, and if you want to change the cache directory, pass --cache-path <PATH>.

It is possible to choose sources to build by specifying multiple path options (can be paths to source directories or files).

Build Modes

There are three build modes:

  • Just compilation (default): Builds the project and saves the contract artifacts in out/ (or the path specified by --out <PATH>).
  • Size mode (--sizes): Builds the project, displays the size of non-test contracts and exits with code 1 if any of them are above the size limit.
  • Name mode (--names): Builds the project, displays the names of the contracts and exits.

The Optimizer

You can enable the optimizer by passing --optimize, and you can adjust the number of optimizer runs by passing --optimizer-runs <RUNS>.

You can also opt-in to the Solidity IR compilation pipeline by passing --via-ir. Read more about the IR pipeline in the Solidity docs.

By default, the optimizer is enabled and runs for 200 cycles.

Conditional Optimizer Usage

Many projects use the solc optimizer, either through the standard compilation pipeline or the IR pipeline. But in some cases, the optimizer can significantly slow down compilation speeds.

A config file for a project using the optimizer may look like this for regular compilation:

solc-version = "0.8.17"
optimizer = true
optimizer-runs = 10_000_000

Or like this for via-ir:

solc-version = "0.8.17"
via_ir = true

To reduce compilation speeds during development and testing, one approach is to have a lite profile that has the optimizer off and use this for development/testing cycle. The updated config file for regular compilation may look like this:

solc-version = "0.8.17"
optimizer = true
optimizer-runs = 10_000_000

optimizer = false

Or like this for via-ir:

solc-version = "0.8.17"
via_ir = true

optimizerSteps = ''

When setup like this, forge build (or forge test / forge script) still uses the standard profile, so by default a forge script invocation will deploy your contracts with the production setting. Running FOUNDRY_PROFILE=lite forge build (and again, same for the test and script commands) will use the lite profile to reduce compilation times.

There are additional optimizer details you can configure, see the Additional Optimizer Settings section below for more info.


You can add extra output from the Solidity compiler to your artifacts by passing --extra-output <SELECTOR>.

The selector is a path in the Solidity compiler output, which you can read more about in the Solidity docs.

You can also write some of the compiler output to separate files by passing --extra-output-files <SELECTOR>.

Valid selectors for --extra-output-files are:

  • metadata: Written as a metadata.json file in the artifacts directory
  • ir: Written as a .ir file in the artifacts directory
  • irOptimized: Written as a .iropt file in the artifacts directory
  • ewasm: Written as a .ewasm file in the artifacts directory
  • evm.assembly: Written as a .asm file in the artifacts directory

Watch Mode

The command can be run in watch mode by passing --watch [PATH...], which will rebuild every time a watched file or directory is changed. The source directory is watched by default.

Sparse Mode (experimental)

Sparse mode only compiles files that match certain criteria.

By default, this filter applies to files that have not been changed since the last build, but for commands that take file filters (e.g. forge test), sparse mode will only recompile files that match the filter.

Sparse mode is opt-in until the feature is stabilized. To opt-in to sparse mode and try it out, set sparse_mode in your configuration file.

Additional Optimizer Settings

The optimizer can be fine-tuned with additional settings. Simply set the optimizer_details table in your configuration file. For example:

constantOptimizer = true
yul = true

stackAllocation = true
optimizerSteps = 'dhfoDgvulfnTUtnIf'

See the compiler input description documentation for more information on available settings (specifically settings.optimizer.details).

Revert Strings

You can control how revert strings are generated by the compiler. By default, only user supplied revert strings are included in the bytecode, but there are other options:

  • strip: Removes all revert strings (if possible, i.e. if literals are used) keeping side-effects.
  • debug: Injects strings for compiler-generated internal reverts, implemented for ABI encoders V1 and V2 for now.
  • verboseDebug: Appends further information to user-supplied revert strings (not yet implemented).

Additional Model Checker settings

Solidity’s built-in model checker is an opt-in module that can be enabled via the ModelChecker object.

See Compiler Input Description settings.modelChecker and the model checker’s options.

The module is available in solc release binaries for OSX and Linux. The latter requires the z3 library version [4.8.8, 4.8.14] to be installed in the system (SO version 4.8).

Similarly to the optimizer settings above, the model_checker settings must be prefixed with the profile they correspond to: [profile.default.model_checker] belongs to the [profile.default].

## foundry.toml
contracts = { '/path/to/project/src/Contract.sol' = [ 'Contract' ] }
engine = 'chc'
timeout = 10000
targets = [ 'assert' ]

The fields above are recommended when using the model checker. Setting which contract should be verified is extremely important, otherwise all available contracts will be verified which can consume a lot of time. The recommended engine is chc, but bmc and all (runs both) are also accepted. It is also important to set a proper timeout (given in milliseconds), since the default time given to the underlying solvers may not be enough. If no verification targets are given, only assertions will be checked.

The model checker will run when forge build is invoked, and will show findings as warnings if any.


Build Options

--names     Print compiled contract names.

--sizes     Print compiled non-test contract sizes, exiting with code 1 if any of them are above the size limit.

--skip     Skip compilation of non-essential contract directories like test or script (usage --skip test).

[PATHS]...    Build source files from specified paths.

Cache Options

    Clear the cache and artifacts folder and recompile.

Linker Options

--libraries libraries
    Set pre-linked libraries.

    The parameter must be in the format <remapped path to lib>:<library name>:<address>, e.g. src/Contract.sol:Library:0x....

    Can also be set in your configuration file as libraries = ["<path>:<lib name>:<address>"].

Compiler Options

    Activate the Solidity optimizer.

--optimizer-runs runs
    The number of optimizer runs.

    Use the Yul intermediate representation compilation pipeline.

    How to treat revert and require reason strings.

--use solc_version
    Specify the solc version, or a path to a local solc, to build with.

    Valid values are in the format x.y.z, solc:x.y.z or path/to/solc.

    Do not access the network. Missing solc versions will not be installed.

    Do not auto-detect solc.

--ignored-error-codes error_codes
    Ignore solc warnings by error code. The parameter is a comma-separated list of error codes.

--extra-output selector
    Extra output to include in the contract's artifact.

    Example keys: abi, storageLayout, evm.assembly, ewasm, ir, ir-optimized, metadata.

    For a full description, see the Solidity docs.

--extra-output-files selector
    Extra output to write to separate files.

    Example keys: abi, storageLayout, evm.assembly, ewasm, ir, ir-optimized, metadata.

    For a full description, see the Solidity docs.

--evm-version version
    The target EVM version.

Project Options

    Generate build info files.

--build-info-path path
    Output path to directory that build info files will be written to.

--root path
    The project's root path. By default, this is the root directory of the current git repository, or the current working directory.

-C path
--contracts path
    The contracts source directory.
    Environment: DAPP_SRC

--lib-paths path
    The path to the library folder.

-R remappings
--remappings remappings
    The project's remappings.

    The parameter is a comma-separated list of remappings in the format <source>=<dest>.

--cache-path path
    The path to the compiler cache.

--config-path file
    Path to the config file.

    This is a convenience flag, and is the same as passing --contracts contracts --lib-paths node-modules.

-o path
--out path
    The project's artifacts directory.

    Suppress all output.

Watch Options

-w [path...]
--watch [path...]
    Watch specific file(s) or folder(s).

    By default, the project's source directory is watched.

-d delay
--delay delay
    File update debounce delay.

    During the delay, incoming change events are accumulated and only once the delay has passed, is an action taken.
    Note that this does not mean a command will be started: if --no-restart is given and a command is already running, the outcome of the action will be to do nothing.

    Defaults to 50ms. Parses as decimal seconds by default, but using an integer with the ms suffix may be more convenient.

    When using --poll mode, you'll want a larger duration, or risk overloading disk I/O.

    Do not restart the command while it's running.

    Explicitly re-run the command on all files when a change is made.

Common Options

    Prints help information.


  1. Build the project:

    forge build
  2. Build the project with solc 0.6.0:

    forge build --use solc:0.6.0
  3. Build the project with additional artifact output:

    forge build --extra-output evm.assembly
  4. Build the project in watch mode:

    forge build --watch
  5. Build source files from test/invariant directory and test/RegressionTest.sol:

    forge build test/invariant test/RegressionTest.sol


forge, forge clean, forge inspect