web3_sha3

web3_sha3 computes the Keccak-256 hash of the hex-encoded data you pass in and returns it as a 32-byte 0x-prefixed string. Despite the method name, this is the original Keccak-256 used throughout the EVM — not the later NIST SHA3-256 standard — which is exactly the hash Polygon and every EVM chain use for event topics and function selectors. Running it on a Polygon node lets you reproduce on-chain hashing without a local crypto library. Send the request to the Polygon mainnet endpoint at https://polygon.therpc.io/YOUR_API_KEY (chain ID 137, 0x89).

Use cases

• Compute event topic hashes — the Keccak-256 of an event signature like Transfer(address,address,uint256) — to build eth_getLogs filters for Polygon contracts such as the USDT token at 0xc2132D05D31c914a87C6611C10748AEb04B58e8F.
• Generate 4-byte function selectors by hashing a function signature and taking the first four bytes, useful when crafting raw calldata for Polygon contract calls.

Parameters

Response

Example request

1curl https://polygon.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 Polygon playground.

Errors & troubleshooting

Common pitfalls

• The input must be hex-encoded bytes, not a raw UTF-8 string. To hash a signature like Transfer(address,address,uint256), encode it to its hex byte representation first — passing the literal string will hash the wrong bytes.
• Keccak-256 is not NIST SHA3-256. Many standard-library "sha3" functions implement the finalized SHA3 and will return different output; use a library that explicitly provides the Ethereum Keccak-256 variant to match Polygon's on-chain results.

Supported networks

• Mainnet — Chain ID: 137
• Amoy — Chain ID: 80002

See also

• eth_call
• eth_getLogs

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