eth_getUncleByBlockNumberAndIndex

eth_getUncleByBlockNumberAndIndex returns the uncle (ommer) block header at a given index within the block at a specified height or block tag. It is the height-addressed twin of eth_getUncleByBlockHashAndIndex and is offered on Arbitrum One — the ETH-fee Optimistic Rollup built on Nitro/ArbOS — purely for Ethereum JSON-RPC compatibility. Because Arbitrum One orders blocks through a single sequencer with no proof-of-work fork race, it never produces uncle blocks, so this method always returns null here whatever block number or index you supply. Point requests at https://arbitrum.therpc.io/YOUR_API_KEY (chain ID 42161, 0xa4b1).

Use cases

• Scan a range of blocks by number to collect uncle headers for uncle-rate analysis; on Arbitrum One every block in the range returns null, since the sequencer produces no ommers.
• Use block tags such as "earliest" to reach genesis-era blocks conveniently without first resolving a hash — though on Arbitrum One even the earliest blocks reference no uncles.

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

Try it live in the Arbitrum One playground.

Errors & troubleshooting

Common pitfalls

• Arbitrum One produces no uncles by design (single sequencer, no PoW competition), so this call returns null for every block — recent or historical — just as post-Merge proof-of-stake chains do.
• Even on chains that do have uncles, an uncle is a header only and contains no transactions array, so do not write code that expects to read transactions from the result here.

Supported networks

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

See also

• eth_getUncleByBlockHashAndIndex
• eth_getUncleCountByBlockNumber
• eth_getBlockByNumber

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_getUncleByBlockNumberAndIndex","params":["","0x0"]}'