Keccak Hash Generator

Keccak-256 hash generator for Ethereum

Keccak is the sponge-based hash that won NIST’s SHA-3 competition. Before the standard was finalised, NIST changed the padding rule, so the published SHA-3 functions differ from the original Keccak. Ethereum had already adopted the original, and it still uses Keccak-256 everywhere. This tool computes original Keccak-224, -256, -384 and -512.

Example: a Solidity function selector

Input (function signature):

transfer(address,uint256)

Keccak-256:

a9059cbb2ab09eb219583f4a59a5d0623ade346d962bcd4e46b11da047c9049b

The first four bytes, a9059cbb, are the function selector for the ERC-20 transfer function — the value that appears at the start of the call data of every token transfer. SHA3-256 of the same text is 4b40e901eada9ab2…, which is why using the wrong function breaks contract calls.

Keccak vs SHA-3

Libraries are not always clearly named: in some JavaScript and Python packages, a function called “sha3” actually computes Keccak-256. When results do not match, this difference is the first thing to check. For the standard version, use SHA3-256.

Common Ethereum uses

• Function selectors: first 4 bytes of keccak256("name(type1,type2)") — no spaces, canonical type names such as uint256.
• Event topics: the full 32-byte hash of the event signature, e.g. Transfer(address,address,uint256).
• Addresses: the last 20 bytes of the Keccak-256 hash of the uncompressed public key (without its 0x04 prefix byte).
• Storage slots and mapping keys in contract storage layout.

To see exactly which bytes a signature string consists of before hashing, convert it with String to Hex.

Text vs bytes

This tool hashes the UTF-8 bytes of the text you type. That is right for signatures such as transfer(address,uint256). To hash binary data such as a public key or ABI-encoded values, the input must be the raw bytes, not their hex text — hashing the string “0xabc…” gives a different result. Developer libraries (ethers.js keccak256, web3.py Web3.keccak) accept byte arrays for that purpose.

Keccak is a fast hash and not a way to protect secrets such as seed phrases or private keys; never paste those into any website. Hashing here happens locally.

Reference values to check your setup

Well-known Ethereum hashes make good test inputs. If the tool, your library and a block explorer all agree on these, you are using the right function:

The most common signature mistakes are writing uint instead of uint256, adding spaces after commas and including parameter names. All three change the hash completely.