web3_sha3

web3_sha3 computes the Keccak-256 hash of the hex-encoded data you pass in and returns the 32-byte digest as a 0x-prefixed string. Despite the method name, this is the original Keccak-256 that Ethereum and every EVM chain rely on — not the later NIST SHA3-256 standard, which produces different output. Because OP Mainnet is an OP Stack EVM rollup that settles to Ethereum L1 and uses ETH for gas, it uses exactly the same hashing as Ethereum, so results match mainnet byte for byte. Call it at https://optimism.therpc.io/YOUR_API_KEY (chain ID 10, 0xa).

Use cases

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

Parameters

Response

Example request

1curl https://optimism.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 Optimism playground.

Errors & troubleshooting

Common pitfalls

• The input must be 0x-prefixed hex-encoded bytes, not a raw UTF-8 string — encode text to hex first, or you will hash the wrong bytes and get a mismatched digest.
• Keccak-256 is not NIST SHA3-256: a standard-library sha3 function can return a different hash unless it specifically implements Ethereum's Keccak variant, so verify your local library matches the on-chain result.

Supported networks

• Mainnet — Chain ID: 10
• Sepolia — Chain ID: 11155420

See also

• eth_call
• eth_getLogs

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