Foundry Integration

Build a Foundry project from scratch, configure it for Cronos EVM, and deploy a sample contract with forge script.

Foundry is a Solidity-native toolchain: tests, deploy scripts and fixtures are all written in Solidity, and there is no Node.js dependency.

Prerequisites

• A wallet private key: With a small amount of CRO to pay for gas fees. (For testnet TCRO, use the faucet at https://faucet.cronos.com/.)

• An RPC endpoint: See details here.

• A Cronos Explorer API key, see how to obtain it here.

Step 1. Install Foundry

Run the following in your terminal:

curl -L https://foundry.paradigm.xyz | bash && foundryup

This installs forge, cast, anvil and chisel.

Verify the installation with:

forge --version

Step 2. Create and initialize the project

forge init my-cronos-project
cd my-cronos-project

Foundry creates the following structure:

my-cronos-project/
├── src/          # Your contracts
├── test/         # Tests
├── script/       # Deployment scripts
└── foundry.toml  # Project configuration

Step 3. Write your contract

forge init creates a sample contract Counter.sol at src/. You can remove it and add your contracts to src/.

Step 3.1. Install Dependencies

For example, to add OpenZeppelin as a dependency:

forge install OpenZeppelin/openzeppelin-contracts@v5.6.0

Then add the remapping to foundry.toml:

[profile.default]
remappings = [    
    "@openzeppelin/=lib/openzeppelin-contracts/",
]

Pin the versions. An unpinned forge install tracks the default branch, so a later forge update can silently change your bytecode — and bytecode that no longer matches is bytecode you cannot verify.

Step 4. Configure .env

Create a .env file in the project root:

PRIVATE_KEY=your_private_key_here
CRONOS_EXPLORER_API_KEY_MAINNET=your_mainnet_api_key_here
CRONOS_EXPLORER_API_KEY_TESTNET=your_testnet_api_key_here

Then load it before running any scripts:

source .env

Check how to get a Cronos Explorer API key here.

Never commit your .env file to version control. Add it to .gitignore to keep your private key safe.

.env holds your private key in plain text. For mainnet work, prefer Foundry's encrypted keystore (cast wallet import) and pass --account <name> instead of relying on PRIVATE_KEY.

Step 5. Configure Cronos

Set the compiler, both RPC aliases and both verification endpoints in foundry.toml , example config:

foundry.toml

[profile.default]
src = "src"
out = "out"
libs = ["lib"]
solc = "0.8.28"
evm_version = "cancun"
optimizer = true
optimizer_runs = 200
remappings = ["@openzeppelin/=lib/openzeppelin-contracts/"]

# Cronos EVM RPC endpoints
[rpc_endpoints]
cronos_mainnet = "https://evm.cronos.com/"
cronos_testnet = "https://evm-t3.cronos.com/"

# Cronos Explorer verification endpoints.
# The API key is passed on the command line with --etherscan-api-key.
[etherscan]
cronos_mainnet = { key = "${CRONOS_EXPLORER_MAINNET_API_KEY}", chain = 25, url = "https://explorer-api.cronos.org/mainnet/api/v2" }
cronos_testnet = { key = "${CRONOS_EXPLORER_TESTNET_API_KEY}", chain = 338, url = "https://explorer-api.cronos.org/testnet/api/v2" }

Foundry has no gasPrice config field, instead it reads the gas price from the node via eth_gasPrice, which is correct on Cronos. If a transaction stalls, override it explicitly with --gas-price 10100000000000 (10,100 gwei) — check the current level at explorer.cronos.com/charts.

Step 6. Compile

forge build

Step 7. Test

forge init creates a sample test for Counter.sol at test/. To run it:

forge test

Step 8. Deploy

Foundry deploys with Solidity scripts, forge init creates a sample script at src/. To run it:

forge script script/Counter.s.sol:CounterScript \
  --rpc-url cronos_testnet \
  --broadcast

--rpc-url cronos_testnet refers to the alias defined in [rpc_endpoints]. Swap it for cronos_mainnet to deploy to mainnet. Drop --broadcast to simulate without sending anything.

Step 9. Verify

Run forge verify-contract after deployment:

forge verify-contract <ADDRESS> src/Counter.sol:Counter \
  --chain-id 338 \
  --verifier-url https://explorer-api.cronos.org/testnet/api/v2 \
  --etherscan-api-key YOUR_CRONOS_EXPLORER_TESTNET_API_KEY \

For contracts that take parameters in contructor, add --constructor-args and cast abi-encode. For example, the verification command for an ERC20 token that takes name and symbol as constructor parameters will look like:

forge verify-contract <ADDRESS> src/MyERC20.sol:MyERC20 \
  --chain-id 338 \
  --verifier-url https://explorer-api.cronos.org/testnet/api/v2 \
  --etherscan-api-key $CRONOS_EXPLORER_TESTNET_API_KEY \
  --constructor-args $(cast abi-encode "constructor(string,string)" "My token name" "My token symbol")