eth_getBlockTransactionCountByHash

eth_getBlockTransactionCountByHash returns the number of transactions in the Arbitrum One block identified by a given 32-byte hash. It is a lightweight way to gauge how full an L2 block is without downloading the full block body — useful on this ETH-gas Optimistic Rollup where the Nitro sequencer packs blocks quickly. Send the hash to https://arbitrum.therpc.io/YOUR_API_KEY (chain ID 42161) and parse the hex count from the response.

Use cases

• Quickly gauge how full an Arbitrum One block is without fetching its full body.
• Validate that a block holds the expected number of transactions after indexing it, as a cheap integrity check.
• Measure L2 throughput across a set of known block hashes to chart Arbitrum One activity over time.

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_getBlockTransactionCountByHash",
7    "params": ["0x0000000000000000000000000000000000000000000000000000000000000000"],
8    "id": 1
9  }'

Try it live in the Arbitrum One playground.

Errors & troubleshooting

Common pitfalls

• Returns null when the block hash is not found on the node — null-check before running parseInt, or you will get NaN.
• When you have a block number rather than a hash and do not need hash-based certainty, use eth_getBlockTransactionCountByNumber instead.

Supported networks

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

See also

• eth_getBlockTransactionCountByNumber
• eth_getBlockByHash
• eth_getTransactionByBlockHashAndIndex

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_getBlockTransactionCountByHash","params":[""]}'