eth_getUncleCountByBlockHash

eth_getUncleCountByBlockHash returns the number of uncle blocks referenced by the block identified by a given block hash, as a hex-encoded integer. On Arbitrum One — the ETH-denominated Optimistic Rollup running Nitro/ArbOS — this count is always "0x0": the chain orders blocks with a single sequencer and has no proof-of-work fork race, so no uncle (ommer) blocks are ever produced. The method is kept for Ethereum JSON-RPC compatibility so existing tooling does not break. Call it at https://arbitrum.therpc.io/YOUR_API_KEY (chain ID 42161, 0xa4b1).

Use cases

• Check whether a block references any uncles before issuing eth_getUncleByBlockHashAndIndex calls; on Arbitrum One the answer is always "0x0", so the follow-up calls can be skipped entirely.
• Build a historical uncle-rate time-series for cross-chain network-health research, recording that Arbitrum One's rate is a constant zero by virtue of its single-sequencer design.

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": "eth_getUncleCountByBlockHash",
7    "params": ["0x0000000000000000000000000000000000000000000000000000000000000000"],
8    "id": 1
9  }'

Try it live in the Arbitrum One playground.

Errors & troubleshooting

Common pitfalls

• On Arbitrum One every block returns "0x0", mirroring post-Merge proof-of-stake chains; this method only ever yields non-zero counts against historical proof-of-work data on other networks.
• An unknown or non-existent block hash returns null rather than a count, so distinguish null (block not found) from "0x0" (block found, no uncles) in your code.

Supported networks

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

See also

• eth_getUncleByBlockHashAndIndex
• eth_getUncleCountByBlockNumber
• eth_getBlockByHash

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":"eth_getUncleCountByBlockHash","params":["0x0000000000000000000000000000000000000000000000000000000000000000"]}'