eth_blockNumber

eth_blockNumber returns the height of the most recently accepted L2 block on OP Mainnet, the OP Stack optimistic rollup that settles to Ethereum and pays gas in ETH. Because OP Mainnet produces a block roughly every 2 seconds, this single integer is the fastest way to know how far the sequencer has advanced. Send the request to https://optimism.therpc.io/YOUR_API_KEY (chain ID 10, 0xa); the response is the latest L2 block number as a hex string.

Use cases

• Heartbeat probe: the cheapest call (1 CU) to confirm your OP Mainnet endpoint is live and the sequencer is producing blocks.
• Anchor the current L2 height before paginating eth_getLogs ranges across historical Optimism blocks.
• Drive a "wait for N confirmations" loop in Velodrome or Synthetix deployment scripts on OP Mainnet.
• Compare the latest height against a target block to judge how close a transaction is to L2 finality.

Parameters

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Response

Example request

1curl https://optimism.therpc.io/YOUR_API_KEY \
2  -X POST \
3  -H "Content-Type: application/json" \
4  -d '{
5    "jsonrpc": "2.0",
6    "method": "eth_blockNumber",
7    "params": [],
8    "id": 1
9  }'

Try it live in the Optimism playground.

Errors & troubleshooting

Common pitfalls

• The result is a hex string such as "0x7a1b3c" — run it through parseInt(value, 16) or BigInt(value) before doing any arithmetic.
• With ~2s OP Mainnet blocks the value moves quickly, but providers cache it briefly; two calls a few milliseconds apart can return the same height.
• This is the OP Mainnet L2 block number, not the Ethereum L1 batch or the block at which that batch was posted — do not confuse the two when reasoning about settlement.

Supported networks

• Mainnet — Chain ID: 10
• Sepolia — Chain ID: 11155420

See also

• eth_getBlockByNumber
• eth_getBlockByHash
• eth_syncing
• eth_chainId

1curl https://optimism.therpc.io/YOUR_API_KEY \
2  -X POST \
3  -H 'Content-Type: application/json' \
4  -d '{"jsonrpc":"2.0","id":1,"method":"eth_blockNumber","params":[]}'