eth_getTransactionByBlockNumberAndIndex

eth_getTransactionByBlockNumberAndIndex returns the transaction at a given position inside a block, with the block addressed by its height or by a tag like latest, finalized, or pending. It's the sibling of the by-hash lookup, but keyed on number instead of hash, which is what you usually want for scanning forward through Ethereum mainnet (chain ID 1, gas paid in ETH) where heights are simple to iterate. Give it a block number and a zero-based hex index, and the node returns the full transaction object sitting at that slot, the same shape eth_getTransactionByHash produces. Querying by number lets you reach symbolic tags like pending that no fixed hash exists for. The endpoint is https://ethereum.therpc.io/YOUR_API_KEY.

Use cases

March block by block pulling index 0x0 from each height to study top-of-block placement, the slot MEV researchers care about most.
Peek at the pending block's contents by index to see what a client expects to include next from the mempool before the slot is sealed.
Scan sequentially over a known height range when you have block numbers in hand and don't need to resolve a hash first — incrementing a counter is cheaper than tracking hashes.

Parameters

#	Name	Type	Required	Description
1	`blockTag`	string	Yes	The block containing the transaction.
2	`transactionIndex`	string (hex)	Yes	Zero-based position of the transaction within the block.

Response

Type	Description
object \| null	Same transaction object as eth_getTransactionByHash. Returns null if block or index 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_getTransactionByBlockNumberAndIndex",
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 is malformed or transaction index is not a valid hex integer.

Common pitfalls

The index is hex-encoded: "0x0" for the first transaction, never a decimal 0. Same goes for higher positions — "0xf", not 15.
The pending block is a client's local guess, not a finalized fact. Its ordering and even which transactions appear differ between geth, erigon, nethermind and besu, so don't treat a pending-tag result as canonical.

Supported networks

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