eth_getTransactionByBlockHashAndIndex

eth_getTransactionByBlockHashAndIndex fetches a single transaction by where it sits, not by what it is. You name a block by its hash and a zero-based position within that block, and Ethereum mainnet (chain ID 1, fees denominated in ETH) returns the full transaction object at that slot. The order matters here: a validator fixes the transaction ordering when it seals the block, and that order is exactly what this index walks. It's the same transaction object you'd get from eth_getTransactionByHash, just addressed positionally. Querying by block hash rather than number means you're pinned to one specific block even across a reorg. Send the call to https://ethereum.therpc.io/YOUR_API_KEY.

Use cases

Walk a block's transactions in order by incrementing the index from 0x0 until you hit null, when you already have the block hash but not the individual tx hashes.
Pull the first transaction in a block to study ordering — the top slot is where MEV searchers and builders fight to land arbitrage and liquidation bundles.
Resolve a transaction by its position reference (block hash plus index) when that's how it was cited, instead of needing its hash up front.

Parameters

#	Name	Type	Required	Description
1	`blockHash`	string (hex)	Yes	The hash of 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_getTransactionByBlockHashAndIndex",
7    "params": [
8        "0x0000000000000000000000000000000000000000000000000000000000000000",
9        "0x0"
10      ],
11    "id": 1
12  }'

Try it live in the Ethereum playground.

Errors & troubleshooting

Code	Message	Cause
`-32602`	`Invalid params`	Block hash or transaction index is malformed.

Common pitfalls

The index is hex, not decimal. The first transaction is "0x0", the eleventh is "0xa" — passing a bare 0 or a decimal 10 will misfire.
Run the index past the block's last transaction and you get null, not an error. Pair this with eth_getBlockTransactionCountByNumber, or just treat null as your stop condition when enumerating.

Supported networks

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