eth_getUncleByBlockNumberAndIndex

eth_getUncleByBlockNumberAndIndex returns the uncle (ommer) block header at a given index inside the block at a specified height or block tag. On OP Mainnet — the ETH-gas OP Stack rollup at chain ID 10 (0xa) that settles to Ethereum L1 — this method is kept for JSON-RPC compatibility but always returns null. Blocks here are produced by a single sequencer roughly every 2 seconds with no proof-of-work competition, so no orphaned sibling blocks (uncles) are ever referenced. You can call it against https://optimism.therpc.io/YOUR_API_KEY with any height and index, and the response will be null.

Use cases

• On a proof-of-work chain you might scan a range of block numbers to collect every uncle header for uncle-rate analysis; on OP Mainnet such a scan returns null at every height because the rollup mints no uncles.
• The earliest tag conveniently targets genesis-era blocks, but OP Mainnet's genesis and all later blocks carry no uncles, so this still yields null — the call remains available only for tooling that expects the standard method to exist.

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_getUncleByBlockNumberAndIndex",
7    "params": [
8        "latest",
9        "0x0"
10      ],
11    "id": 1
12  }'

Try it live in the Optimism playground.

Errors & troubleshooting

Common pitfalls

• OP Mainnet's OP Stack consensus produces no uncles at any height — not just recent blocks — so this method always returns null. Do not interpret that null as the block being missing or the request being wrong.
• Even on chains that produce uncles, an uncle is a header only and carries no transactions array; never expect transaction data back from this method.

Supported networks

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

See also

• eth_getUncleByBlockHashAndIndex
• eth_getUncleCountByBlockNumber
• 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_getUncleByBlockNumberAndIndex","params":["","0x0"]}'