web3_sha3

web3_sha3 computes the Keccak-256 hash of the hex-encoded data you pass in and returns it as a 0x-prefixed 32-byte value. Despite the sha3 in its name, it is the original Keccak-256 used throughout Ethereum — not the later NIST SHA3-256 standard, which produces different output for the same input. Arbitrum One (chain ID 42161) is EVM-equivalent — an Optimistic Rollup that settles to Ethereum and pays gas in ETH — so it hashes exactly as L1 does, and the result from https://arbitrum.therpc.io/YOUR_API_KEY matches what your contracts and tooling compute locally. This is a pure utility call: it touches no chain state and takes a single hex-string parameter.

Use cases

• Compute event topic hashes — the Keccak-256 of an event signature string such as Transfer(address,address,uint256) — to build topics filters for eth_getLogs against Arbitrum One contracts like Uniswap or Aave.
• Generate 4-byte function selectors by hashing a function signature and taking the first four bytes of the digest, useful when crafting or decoding calldata on Arbitrum One.

Parameters

Response

Example request

1curl https://arbitrum.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 Arbitrum One playground.

Errors & troubleshooting

Common pitfalls

• The input must be 0x-prefixed hex-encoded bytes, not a raw UTF-8 string. To hash a signature like Transfer(address,address,uint256), encode it to hex first — passing the literal text yields the hash of the wrong bytes.
• Keccak-256 is not SHA3-256. A standard library sha3 function may return a different digest unless it specifically implements the Ethereum Keccak variant, so confirm your local hashing matches before relying on it interchangeably with this method.

Supported networks

• Mainnet — Chain ID: 42161
• Sepolia — Chain ID: 421614

See also

• eth_call
• eth_getLogs

1curl https://arbitrum.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"]}'