eth_getTransactionByBlockHashAndIndex

eth_getTransactionByBlockHashAndIndex fetches a single transaction by its position inside a block, where the block is named by its hash, on Arbitrum One. Arbitrum One (chain ID 42161) is an Optimistic Rollup where the Nitro sequencer fixes transaction ordering and gas is paid in ETH, so the index reflects the sequencer's deterministic order. Send the block hash 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 does not exist.

Use cases

• Enumerate every transaction in a specific Arbitrum One block by stepping the index from 0x0 upward.
• Retrieve the first transaction in a block to study the sequencer's ordering and any MEV positioning.
• Resolve a transaction from a block-and-position reference when you have the block hash but not the transaction hash.

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

Try it live in the Arbitrum One playground.

Errors & troubleshooting

Common pitfalls

• The index is hex-encoded — pass "0x0" for the first transaction, not the integer 0.
• If the index is at or beyond the block's transaction count the method returns null, so null-check before reading fields.

Supported networks

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

See also

• eth_getTransactionByHash
• eth_getTransactionByBlockNumberAndIndex
• eth_getBlockByHash
• eth_getTransactionReceipt

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_getTransactionByBlockHashAndIndex","params":["0x0000000000000000000000000000000000000000000000000000000000000000","0x0"]}'