web3_sha3

web3_sha3 hashes a chunk of hex-encoded data with Keccak-256 and hands back the 32-byte digest. The name is a historical trap: despite "sha3", this is the original Keccak-256, not the NIST SHA3-256 that FIPS-202 later standardised with different padding. Ethereum settled on the pre-standard Keccak everywhere — it is the function behind address derivation, event topics, function selectors, and Merkle-Patricia trie keys — which is exactly why the node exposes it here. Send the data to https://ethereum.therpc.io/YOUR_API_KEY on mainnet (chain ID 1) and you get the canonical ETH-flavoured hash without needing a local crypto library. The input must be a 0x-prefixed hex string, and the output is a 0x-prefixed 64-character hex digest.

Use cases

• Derive the topic hash for a log filter by hashing an event signature like Transfer(address,address,uint256), then drop the result into an eth_getLogs query against an ERC-20 contract.
• Build a 4-byte function selector by hashing a function signature such as transfer(address,uint256) and taking the first four bytes of the Keccak-256 digest — the same value an EVM call places at the start of its calldata.

Parameters

Response

Example request

1curl https://ethereum.therpc.io/YOUR_API_KEY \
2  -X POST \
3  -H "Content-Type: application/json" \
4  -d '{
5    "jsonrpc": "2.0",
6    "method": "web3_sha3",
7    "params": ["0x"],
8    "id": 1
9  }'

Try it live in the Ethereum playground.

Errors & troubleshooting

Common pitfalls

• The input is interpreted as raw hex bytes, not text. To hash a string like an event signature, encode it to UTF-8 bytes and then to hex first; passing the literal characters will hash the wrong thing.
• Keccak-256 is not SHA3-256. A standard-library sha3_256 will give a different digest because of the padding change introduced when Keccak became FIPS-202. Reach for a library that explicitly offers the Ethereum Keccak variant (for example keccak256 in viem or ethers), or just let this method compute it for you.

Supported networks

• Mainnet — Chain ID: 1
• Sepolia — Chain ID: 11155111

See also

• eth_call
• eth_getLogs

1curl https://ethereum.therpc.io/YOUR_API_KEY \
2  -X POST \
3  -H 'Content-Type: application/json' \
4  -d '{"jsonrpc":"2.0","id":1,"method":"web3_sha3","params":["0x"]}'