eth_getUncleByBlockHashAndIndex

eth_getUncleByBlockHashAndIndex is the standard Ethereum JSON-RPC call that returns the uncle (ommer) block header at a given index within the block identified by a block hash. It exists on Arbitrum One — the ETH-denominated Optimistic Rollup running Nitro/ArbOS — for API compatibility, but Arbitrum One produces no uncle blocks: a single sequencer orders transactions and there is no proof-of-work fork race, so no ommers are ever referenced. As a result this method always returns null on Arbitrum One regardless of the block hash or index you pass. The endpoint is https://arbitrum.therpc.io/YOUR_API_KEY (chain ID 42161, 0xa4b1).

Use cases

• Compute uncle reward amounts for historical mining analysis — note that on Arbitrum One there are no uncles and no mining rewards, so this is only meaningful against proof-of-work chains.
• Measure historical uncle rates as a proxy for network latency and mining competition; on Arbitrum One the sequencer model means the uncle rate is structurally zero.
• Retrieve uncle header data for cross-chain blockchain research, keeping in mind that calls here on Arbitrum One return null and yield no header to analyze.

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_getUncleByBlockHashAndIndex",
7    "params": [
8        "0x0000000000000000000000000000000000000000000000000000000000000000",
9        "0x0"
10      ],
11    "id": 1
12  }'

Try it live in the Arbitrum One playground.

Errors & troubleshooting

Common pitfalls

• Even where uncles exist, an uncle is only a header — it carries no transactions array, so never expect transaction data back from this call.
• Arbitrum One never produces uncles at all (single sequencer, no PoW fork race), so every query here returns null for any block; the same is true of post-Merge proof-of-stake chains generally.
• On the proof-of-work chains where this method does return data, a block references at most two uncles, so an index of "0x2" or higher always returns null. On Arbitrum One even index "0x0" is null.

Supported networks

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

See also

• eth_getUncleByBlockNumberAndIndex
• eth_getUncleCountByBlockHash
• 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_getUncleByBlockHashAndIndex","params":["0x0000000000000000000000000000000000000000000000000000000000000000","0x0"]}'