Smart Contract Method ID Finder
Look up smart contract method signatures by their 4-byte method ID
Enter the first 4 bytes of a function selector to look it up
Common Examples
How it works: This tool searches the 4byte.directory database, which maintains a registry of Ethereum function signatures and their corresponding 4-byte method IDs. Click "Search" to open results in a new tab.
1. What is a Method ID?
A method ID (or function selector) is the first 4 bytes of the Keccak-256 hash of a function signature. It's used to identify which function to call in a smart contract transaction.
2. How does it work?
4byte.directory
4byte.directory is a community-maintained database of Ethereum function signatures. When you see an unknown method ID in a transaction, you can look it up here to find the human-readable function signature.
Use Cases
- Identify unknown function calls in transactions
- Reverse-engineer contract interactions
- Understand what a transaction is trying to do
- Verify function signatures match expected values
3. Examples
ERC-20 transfer
0xa9059cbb → transfer(address,uint256)ERC-20 approve
0x095ea7b3 → approve(address,uint256)ERC-20 transferFrom
0x23b872dd → transferFrom(address,address,uint256)