eth_getUncleCountByBlockNumber

eth_getUncleCountByBlockNumber returns the number of uncle blocks referenced by the block at a given height or block tag. On OP Mainnet — the ETH-gas OP Stack rollup at chain ID 10 (0xa) that settles to Ethereum L1 — that count is always 0x0. The chain is built by a single sequencer with no proof-of-work competition, so no orphaned sibling blocks ever become uncles. Point the call at https://optimism.therpc.io/YOUR_API_KEY with any height or tag such as latest, and it returns zero uncles; the method is retained purely for Ethereum JSON-RPC compatibility.

Use cases

• On proof-of-work chains you would scan a sequential range of block numbers to compute an uncle rate; on OP Mainnet each block in the range returns 0x0, so the resulting rate is flat zero.
• Use it as a quick pre-check before calling eth_getUncleByBlockNumberAndIndex — though on OP Mainnet the 0x0 answer tells you upfront there are no uncle details to fetch.

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_getUncleCountByBlockNumber",
7    "params": ["latest"],
8    "id": 1
9  }'

Try it live in the Optimism playground.

Errors & troubleshooting

Common pitfalls

• OP Mainnet always returns 0x0 regardless of which block or tag you query — its OP Stack consensus produces no uncles, so never branch on a non-zero count here.
• The result is a hex-encoded string ("0x0"), not a number — parse it (for example parseInt(result, 16)) before doing any numeric comparison.

Supported networks

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

See also

• eth_getUncleByBlockNumberAndIndex
• eth_getUncleCountByBlockHash
• eth_getBlockByNumber

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_getUncleCountByBlockNumber","params":[""]}'