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Monad Foundry is a custom fork of Foundry that integrates Monad features directly into the familiar Foundry developer workflow. It uses monad-revm, to ensure that forge test, forge script, cast, anvil, and chisel all execute with Monad’s gas model, opcode pricing, and precompile behavior — so your local development environment matches Monad’s on-chain behavior. For general Foundry usage (writing tests, scripts, deployments, configuration, cheatcodes), refer to the Foundry Docs.

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Installation

Install the Monad Foundry installer:
Then install Monad Foundry:
This installs all four binaries — forge, cast, anvil, and chisel — with Monad support.
The same installer also supports standard Foundry. Running foundryup without --network monad will install the official upstream Foundry release, so you can use both side by side.

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Features

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Monad EVM Execution

forge test and forge script execute with Monad EVM by default. The following differences from Ethereum are applied automatically:
  • Gas charging: Gas is charged based on gas_limit, not gas_used. There are no gas refunds. See Gas Pricing for details.
  • Contract size: Max contract size is 128KB
  • Initcode size: Max initcode size is 256KB
  • Precompile gas costs: See Opcode Pricing.
  • No blob transactions: EIP-4844 (type 3) transactions are not supported.
For the complete list of differences, see Differences between Monad and Ethereum.

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Staking Precompile Support

All staking precompile view functions work in forge test at address 0x1000:

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Trace Decoding

When running tests with verbose output (forge test -vvvv), staking calls are decoded with human-readable function names and parameters. The address 0x1000 is labeled as “Staking” in trace output. All staking state-changing functions (addValidator, delegate, undelegate, withdraw, compound, claimRewards, changeCommission, externalReward) and events (ValidatorRewarded, Delegate, Undelegate, Withdraw, ClaimRewards, CommissionChanged, EpochChanged, ValidatorStatusChanged) are decoded in traces. Example trace output:

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Anvil with Monad EVM

Use anvil --monad to run a local development node with Monad EVM:
Monad EVM activates automatically when forking a Monad RPC endpoint (detected via chain ID), so you don’t need the --monad flag when forking.

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Cast & Chisel

cast and chisel execute with Monad EVM by default. All standard commands work the same as upstream Foundry.

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CI Integration

Use the Monad Foundry GitHub Action to install Monad Foundry in your CI workflows:
This installs the latest stable Monad Foundry (stable-monad) by default. You can also pin a specific version:
Full workflow example:
The action supports caching and works on all platforms (Linux, macOS, Windows). See the foundry-toolchain repo for all available options.

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Releases & Versioning

Monad Foundry uses a v{upstream}-monad.{monad_version} versioning scheme. For example, v1.5.0-monad.0.1.0 is based on upstream Foundry v1.5.0 with Monad fork version 0.1.0. See the GitHub Releases for full release history.