eth_getTransactionByBlockNumberAndIndex

eth_getTransactionByBlockNumberAndIndex returns one transaction by its position inside a block, where the block is named by its number or by a tag like latest. On Arbitrum One (chain ID 42161), an Optimistic Rollup paying gas in ETH and settling to Ethereum L1, this is convenient when you are scanning forward by block height rather than tracking hashes. Send a block tag and a hex index to https://arbitrum.therpc.io/YOUR_API_KEY and it returns the transaction at that index position within the block, or null if the block or index is not found.

Use cases

• Walk block-by-block over the first transaction in each Arbitrum One block to study sequencer ordering and MEV.
• Peek at a transaction the sequencer is queuing for the next block by passing the pending tag with a position index.
• Scan blocks sequentially by height when you already have block numbers and do not need to resolve hashes first.

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

Try it live in the Arbitrum One playground.

Errors & troubleshooting

Common pitfalls

• The index is hex-encoded — use "0x0", not the integer 0, for the first transaction.
• Results under the pending tag depend on the sequencer's current view; ordering and availability of pending transactions can differ between calls and node clients, so do not treat them as final.

Supported networks

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

See also

• eth_getTransactionByBlockHashAndIndex
• eth_getTransactionByHash
• 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_getTransactionByBlockNumberAndIndex","params":["",""]}'