Crypto Evm Swiss Knife

---
author: luo-kai
name: crypto-evm-swiss-knife
description: Interact with EVM-compatible blockchains using Foundry's cast tool for querying balances, calling contracts, sending transactions, and blockchain exploration. Use when needing to interact with Ethereum Virtual Machine networks via command-line, including reading contract state, sending funds, executing contract functions, or inspecting blockchain data.
---

# EVM Swiss Knife

This skill enables interaction with EVM-compatible blockchains through Foundry's `cast` command-line tool. It covers common blockchain operations like balance queries, contract calls, transaction sending, and network inspection.

## Installation

To use this skill, you need Foundry installed, which provides the `cast` command.

Follow the official installation guide: https://getfoundry.sh/introduction/installation

### Quick Install (Linux/Mac)

1. Install Foundryup:
   ```bash
   curl -L https://foundry.paradigm.xyz | bash
   ```

2. Source your shell configuration or start a new terminal:
   ```bash
   source ~/.bashrc  # or ~/.zshrc
   ```

3. Install Foundry:
   ```bash
   foundryup
   ```

4. Verify installation:
   ```bash
   cast --version
   ```

For other platforms or detailed instructions, see the full guide at https://getfoundry.sh/introduction/installation

## Prerequisites

- Foundry installed (`cast` command available)
- RPC endpoint configured (via `--rpc-url` or environment variables)
- Private key for transaction operations (if sending txs)

## RPC URL Selection

To interact with different EVM networks, you need reliable RPC endpoints. Use ChainList's API at https://chainlist.org/rpcs.json to get a comprehensive JSON list of RPC URLs for all supported chains.

### How to Select RPC URLs:

1. Fetch the RPC data:
   ```bash
   curl -s https://chainlist.org/rpcs.json | jq '.[] | select(.chainId == 1)'  # For Ethereum (chain ID 1)
   ```

2. Look for RPC URLs that are:
   - **Public and free**: No API keys required
   - **No or limited tracking**: Avoid URLs with "tracking": "yes"
   - **Fast and reliable**: Prefer URLs with low latency or high score
   - **Open source**: Prefer community-maintained endpoints

3. Popular choices (extracted from ChainList):
   - Ethereum (ID 1): https://ethereum-rpc.publicnode.com
   - BNB Smart Chain (ID 56): https://bsc-dataseed.binance.org
   - Base (ID 8453): https://mainnet.base.org
   - Polygon (ID 137): https://polygon-rpc.com

4. For production use, consider paid RPC services like Alchemy, Infura, or QuickNode for higher reliability and rate limits.

5. Always verify the chain ID matches your intended network to avoid connecting to wrong chains.

## Common Operations

### Query Account Balance

Get ETH balance of an address:
```bash
cast balance <address> --rpc-url <rpc_url>
```

Get ERC20 token balance:
```bash
cast call <token_contract> "balanceOf(address)(uint256)" <address> --rpc-url <rpc_url>
```

### Call Contract Functions (Read-Only)

Call a view/pure function:
```bash
cast call <contract_address> "<function_signature>" [args...] --rpc-url <rpc_url>
```

Example - get token total supply:
```bash
cast call 0xA0b86a33E6441e88C5F2712C3E9b74B6F3f5a8b8 "totalSupply()(uint256)" --rpc-url <rpc_url>
```

### Send Transactions

Send ETH:
```bash
cast send --private-key <pk> --rpc-url <rpc_url> <to_address> --value <amount_in_wei>
```

Call contract function (write):
```bash
cast send --private-key <pk> --rpc-url <rpc_url> <contract_address> "<function_signature>" [args...]
```

### Blockchain Inspection

Get latest block number:
```bash
cast block-number --rpc-url <rpc_url>
```

Get block details:
```bash
cast block <block_number> --rpc-url <rpc_url>
```

Get transaction details:
```bash
cast tx <tx_hash> --rpc-url <rpc_url>
```

### Contract Deployment

Deploy a contract:
```bash
cast send --private-key <pk> --rpc-url <rpc_url> --create <bytecode> [constructor_args...]
```

### Decoding Data

Decode hex data:
```bash
cast --to-ascii <hex_string>
cast --to-dec <hex_string>
```

## Network-Specific Examples

### Ethereum Mainnet
```bash
export ETH_RPC_URL=https://eth-mainnet.alchemyapi.io/v2/YOUR_API_KEY
cast balance 0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045
```

### Polygon
```bash
cast balance <address> --rpc-url https://polygon-rpc.com/
```

### Local Development (Anvil)
```bash
cast balance <address> --rpc-url http://127.0.0.1:8545
```

## Error Handling

- RPC errors: Check endpoint URL and network connectivity
- Insufficient funds: Ensure account has enough ETH for gas + value
- Contract errors: Verify function signatures and parameter types
- Private key errors: Ensure correct format (0x prefixed hex)

## Advanced Usage

### Batch Operations
Use shell loops for multiple queries:
```bash
for addr in addr1 addr2 addr3; do
  echo "Balance of $addr: $(cast balance $addr --rpc-url $RPC_URL)"
done
```

### Gas Estimation
Estimate gas for a transaction:
```bash
cast estimate --rpc-url <rpc_url> <to_address> --value <amount>
```

### ABI Interactions
For complex contracts, save ABI to file and use:
```bash
cast call --abi <abi_file> <contract> <function> [args...]
```

## Security Notes

- Never expose private keys in scripts or logs
- Use environment variables for sensitive data
- Test on testnets before mainnet operations
- Verify contract addresses and function signatures
- Monitor gas prices for transaction timing