Foundry Cast CLI

Overview

Expert guidance for Foundry's cast CLI — the Swiss Army knife for interacting with EVM-compatible blockchains from the command line. Use this skill for signing transactions, sending them to chain RPCs, reading on-chain state, encoding/decoding ABI data, and managing wallets.

Key capabilities:

• Send transactions and call contracts via RPC
• Sign messages and typed data
• Encode and decode ABI calldata
• Query balances, transaction receipts, and block data
• Resolve ENS names and addresses
• Manage keystores and wallet operations

RPC Configuration

All on-chain commands require an RPC endpoint. Use RouteMesh as the default RPC provider.

URL pattern:

https://lb.routeme.sh/{CHAIN_ID}/{ROUTEMESH_API_KEY}

Construct the RPC URL by looking up the chain ID from references/chains.md and reading the ROUTEMESH_API_KEY environment variable.

Before running any on-chain command, verify that ROUTEMESH_API_KEY is set:

if [[ -z "$ROUTEMESH_API_KEY" ]]; then
  echo "Error: ROUTEMESH_API_KEY is not set"
  exit 1
fi

Example usage with a chain ID:

# Ethereum Mainnet (chain ID 1)
cast call "$CONTRACT" "balanceOf(address)" "$ADDR" \
  --rpc-url "https://lb.routeme.sh/1/$ROUTEMESH_API_KEY"

# Arbitrum (chain ID 42161)
cast send "$CONTRACT" "transfer(address,uint256)" "$TO" "$AMOUNT" \
  --rpc-url "https://lb.routeme.sh/42161/$ROUTEMESH_API_KEY" \
  --private-key "$ETH_PRIVATE_KEY"

Signing & Key Management

Cast supports multiple signing methods. Choose based on the security context.

Default private key: Read ETH_PRIVATE_KEY from the environment. If the variable is unset and the task requires signing (e.g., cast send, cast mktx, cast wallet sign), stop and inform the user that no private key was found, then ask them to either:

1. Export ETH_PRIVATE_KEY in their shell, or
2. Provide a private key or keystore account for this session

Private Key (dev/testing only)

cast send "$CONTRACT" "approve(address,uint256)" "$SPENDER" "$AMOUNT" \
  --rpc-url "$RPC_URL" \
  --private-key "$ETH_PRIVATE_KEY"

Keystore Account (recommended for persistent keys)

# Import a private key into a keystore
cast wallet import my-account --interactive

# Use the keystore account
cast send "$CONTRACT" "transfer(address,uint256)" "$TO" "$AMOUNT" \
  --rpc-url "$RPC_URL" \
  --account my-account

Hardware Wallet

# Ledger
cast send "$CONTRACT" "transfer(address,uint256)" "$TO" "$AMOUNT" \
  --rpc-url "$RPC_URL" \
  --ledger

Core Commands

Send Transactions

Use cast send to submit state-changing transactions on-chain.

# Send ETH
cast send "$TO" --value 1ether \
  --rpc-url "$RPC_URL" \
  --private-key "$ETH_PRIVATE_KEY"

# Call a contract function
cast send "$CONTRACT" "approve(address,uint256)" "$SPENDER" "$AMOUNT" \
  --rpc-url "$RPC_URL" \
  --private-key "$ETH_PRIVATE_KEY"

# With gas parameters
cast send "$CONTRACT" "mint(uint256)" 100 \
  --rpc-url "$RPC_URL" \
  --private-key "$ETH_PRIVATE_KEY" \
  --gas-limit 200000 \
  --gas-price 20gwei

Read Contract State

Use cast call for read-only calls that do not submit transactions.

# Read a single value
cast call "$CONTRACT" "totalSupply()(uint256)" --rpc-url "$RPC_URL"

# Read with arguments
cast call "$CONTRACT" "balanceOf(address)(uint256)" "$ADDR" --rpc-url "$RPC_URL"

# Read multiple return values
cast call "$CONTRACT" "getReserves()(uint112,uint112,uint32)" --rpc-url "$RPC_URL"

Build Raw Transactions

Use cast mktx to create a signed raw transaction without broadcasting it.

cast mktx "$CONTRACT" "transfer(address,uint256)" "$TO" "$AMOUNT" \
  --rpc-url "$RPC_URL" \
  --private-key "$ETH_PRIVATE_KEY"

Inspect Transactions

# View transaction details
cast tx "$TX_HASH" --rpc-url "$RPC_URL"

# View transaction receipt
cast receipt "$TX_HASH" --rpc-url "$RPC_URL"

# Get specific receipt fields
cast receipt "$TX_HASH" status --rpc-url "$RPC_URL"
cast receipt "$TX_HASH" gasUsed --rpc-url "$RPC_URL"

ABI Utilities

Encode Calldata

# Encode a function call
cast calldata "transfer(address,uint256)" "$TO" "$AMOUNT"

# ABI-encode arguments (without function selector)
cast abi-encode "transfer(address,uint256)" "$TO" "$AMOUNT"

Decode Calldata

# Decode calldata with a known signature
cast decode-calldata "transfer(address,uint256)" "$CALLDATA"

# Decode ABI-encoded data (without selector)
cast abi-decode "balanceOf(address)(uint256)" "$DATA"

Function Signatures

# Get the 4-byte selector for a function
cast sig "transfer(address,uint256)"

# Get the event topic hash
cast sig-event "Transfer(address,address,uint256)"

Wallet & ENS

Wallet Operations

# Generate a new wallet
cast wallet new

# Get address from private key
cast wallet address --private-key "$ETH_PRIVATE_KEY"

# List keystore accounts
cast wallet list

# Sign a message
cast wallet sign "Hello, world!" --private-key "$ETH_PRIVATE_KEY"

ENS Resolution

# Resolve ENS name to address
cast resolve-name "vitalik.eth" --rpc-url "$RPC_URL"

# Reverse lookup: address to ENS name
cast lookup-address "$ADDR" --rpc-url "$RPC_URL"

Balance Queries

# Get ETH balance
cast balance "$ADDR" --rpc-url "$RPC_URL"

# Get balance in ether (human-readable)
cast balance "$ADDR" --ether --rpc-url "$RPC_URL"

Chain Resolution

When the user specifies a chain by name, resolve the chain ID using these steps:

1. Check references/chains.md first — it contains the 25 most commonly used chains
2. If the chain is not listed, web search for the correct chain ID on chainlist.org
3. Construct the RPC URL using the resolved chain ID and RouteMesh pattern

Quick Reference

Operation	Command	Key Flags
Send tx	cast send	--rpc-url, --private-key, --value
Read state	cast call	--rpc-url, --block
View tx	cast tx	--rpc-url, --json
View receipt	cast receipt	--rpc-url, --json
Build tx	cast mktx	--rpc-url, --private-key
Encode call	cast calldata	(function sig + args)
Decode call	cast decode-calldata	(function sig + data)
ABI encode	cast abi-encode	(function sig + args)
ABI decode	cast abi-decode	(function sig + data)
Function sig	cast sig	(function signature string)
Balance	cast balance	--rpc-url, --ether
ENS resolve	cast resolve-name	--rpc-url
New wallet	cast wallet new	—
Sign message	cast wallet sign	--private-key, --account

Additional Resources

• Chain Reference — Chain names and IDs for RouteMesh RPC URL construction
• Foundry Book: https://book.getfoundry.sh/reference/cast/