eth_getUncleByBlockNumberAndIndex

eth_getUncleByBlockNumberAndIndex is the by-height twin of the hash-based uncle lookup: you give it a block number (or a tag like earliest) and the uncle's index, and it returns that ommer's header. Because you address the block by its position in the chain rather than by a 32-byte hash, this is the variant you reach for when walking a contiguous range of Ethereum history to harvest uncles. The data only exists for the Proof-of-Work era. After The Merge at block 15537393, every slot yields a single PoS block with no ommers, so a query against a recent height resolves to null. Call it on https://ethereum.therpc.io/YOUR_API_KEY (chain ID 1); the payload is the uncle's header, no transactions attached.

Use cases

Iterate over a numeric range of pre-Merge blocks (everything below 15537393) and collect every uncle header to compute an uncle-rate curve across Ethereum's PoW years.
Reach early chain history with the earliest tag instead of hardcoding genesis-adjacent heights, which keeps a backfill script readable when crawling the oldest uncles.

Parameters

#	Name	Type	Required	Description
1	`blockTag`	string	Yes	The block that references the uncle.
2	`uncleIndex`	string (hex)	Yes	Zero-based index of the uncle within the block's uncles array.

Response

Type	Description
object \| null	Same uncle header object as eth_getUncleByBlockHashAndIndex. Returns null if not found.

Example request

1curl https://ethereum.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 Ethereum playground.

Errors & troubleshooting

Code	Message	Cause
`-32602`	`Invalid params`	Block tag or uncle index is malformed.

Common pitfalls

Pointing this at latest or any post-Merge height returns null every time, because PoS Ethereum simply does not produce ommers. Keep your scan bounded below block 15537393 to avoid wasting calls.
The header you get back has no transactions array. An uncle's transactions never entered the canonical chain, so there is nothing transactional to decode from the result.

Supported networks

Mainnet — Chain ID: 1
Sepolia — Chain ID: 11155111