eth_getUncleCountByBlockHash

eth_getUncleCountByBlockHash returns the number of uncle blocks referenced by the block identified by a given hash. On OP Mainnet — the ETH-gas OP Stack rollup at chain ID 10 (0xa) — that count is always 0x0. A single sequencer builds the chain with no proof-of-work race, so no orphaned sibling blocks are ever folded in as uncles. The method stays available at https://optimism.therpc.io/YOUR_API_KEY for clients that expect the standard Ethereum JSON-RPC surface, but for any valid OP Mainnet block hash it reports zero uncles.

Use cases

• Normally you would call this first to check whether a block has uncles before issuing eth_getUncleByBlockHashAndIndex calls; on OP Mainnet it always returns 0x0, so those follow-up calls would all yield null.
• Building a historical uncle-rate time-series for network-health research works on proof-of-work chains, but on OP Mainnet every sample is zero — the single-sequencer design leaves no uncle-rate signal to track.

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

Try it live in the Optimism playground.

Errors & troubleshooting

Common pitfalls

• OP Mainnet blocks always return 0x0. This method is only meaningful on proof-of-work history, which OP Mainnet has never had, so do not build logic that expects a non-zero count here.
• For a block hash that the node does not recognize, the result is null rather than 0x0 — so distinguish "unknown block" (null) from "known block with no uncles" (0x0).

Supported networks

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

See also

• eth_getUncleByBlockHashAndIndex
• eth_getUncleCountByBlockNumber
• eth_getBlockByHash

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