Creation Bytecode vs Runtime Bytecode

Nov 6, 2025

Understanding the difference between creation and runtime bytecode is crucial for contract deployment and analysis.

TL;DR 

Deployment Input = Creation Bytecode + Constructor Args (ABI-encoded)
                   └─ From compiler    └─ You append this

Creation bytecode does NOT include constructor arguments.

Quick Reference

Bytecode TypeContainsUse Case
CreationInit logic + Runtime codeforge inspect Contract bytecode
RuntimeFinal on-chain codecast code <address>

Deployment Hex Pattern 

0x[CREATION_CODE][CONSTRUCTOR_ARGS]
  └─ Fixed length  └─ Variable (32 bytes per param)

Example 

# Contract: constructor(uint256 supply, address owner)

CREATION=$(forge inspect MyToken bytecode)
# 0x608060405234801561001057600080fd5b50...

ARGS=$(cast abi-encode "constructor(uint256,address)" 1000000 0x742d35Cc6634C0532925a3b844Bc454e4438f44e)
# 0x00000000000000000000000000000000000000000000000000000000000f4240
#   000000000000000000000000742d35cc6634c0532925a3b844bc454e4438f44e

# Deploy (remove 0x from args)
cast send --create "${CREATION}${ARGS:2}" --rpc-url <RPC> --private-key <KEY>

Hex Breakdown 

0x608060405234801561001057600080fd5b50...  ← Creation bytecode
  00000000000000000000000000000000000000000000000000000000000f4240  ← uint256 (32 bytes)
  000000000000000000000000742d35cc6634c0532925a3b844bc454e4438f44e  ← address (32 bytes, left-padded)

Clone Existing Contract

Deployment tx input already has both parts - use directly:

# 1. Find deployment tx (Etherscan/Sourcify)
# 2. Extract full bytecode
FULL=$(cast tx <DEPLOY_TX> input --rpc-url <RPC>)

# 3. Deploy (args already included)
cast send --create $FULL --rpc-url http://localhost:8545 --private-key <KEY>

Example: Multicall3 

# Contract: 0xcA11bde05977b3631167028862bE2a173976CA11
# No constructor args - only creation bytecode

TX="0x4f0a3c5bb2dcb0420c54838830c894f09e10f0e59d91b0d19cb2d4c234cb2c2f"
BYTECODE=$(cast tx $TX input --rpc-url https://eth.llamarpc.com)

cast send --create $BYTECODE --rpc-url http://localhost:8545 --private-key <KEY>

Common Mistakes 

# ❌ Using runtime bytecode
cast send --create $(cast code 0xAddress)

# ❌ Forgetting constructor args
cast send --create $(forge inspect MyContract bytecode)

# ❌ Not removing 0x prefix
DEPLOY="${CREATION}${ARGS}"  # Double 0x

# ✅ Correct
DEPLOY="${CREATION}${ARGS:2}"

Key Points

  1. Creation ≠ Deployment

    • Compiler outputs creation bytecode
    • You must append ABI-encoded constructor args

  2. Constructor args pattern

    • Each uint256/address = 32 bytes (64 hex chars)
    • Addresses are left-padded with zeros

  3. Cloning contracts

    • Get deployment tx input via Sourcify/Etherscan
    • Contains both creation code + args, ready to use

  4. Why cast creation fails

    • Needs RPC trace APIs (rarely available)
    • Use block explorers instead

Resources