eth_syncing

eth_syncing reports whether the Arbitrum One node behind https://arbitrum.therpc.io/YOUR_API_KEY (chain ID 42161) is still catching up to the chain head or fully synced. Arbitrum One is an Optimistic Rollup whose Nitro nodes replay the sequencer's transaction feed to rebuild L2 state, and a node that has just started must process that backlog before it can serve accurate data. The method returns false when the node is fully synced and tracking the latest block, or an object with startingBlock, currentBlock, and highestBlock (all hex) while it is still importing. Gas on this chain is paid in ETH, so an out-of-sync node can quote stale balances or fee data — making this a cheap pre-flight check before you trust its responses.

Use cases

• Verify a freshly started Arbitrum Nitro node has finished replaying the sequencer feed before you route production traffic to it.
• Display a sync progress percentage in a node-monitoring dashboard by comparing currentBlock against highestBlock.
• Gate application startup on sync completion so your service does not serve stale L2 balances or nonces while the node is still importing.
• Diagnose a stuck or slow node by polling currentBlock over time — if it stops advancing while the network keeps producing blocks, the node has fallen behind the Arbitrum sequencer.

Parameters

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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_syncing",
7    "params": [],
8    "id": 1
9  }'

Try it live in the Arbitrum One playground.

Errors & troubleshooting

Common pitfalls

• Some clients can return false during specific sync phases even when not fully caught up, so do not treat a single false as an absolute guarantee — cross-check currentBlock against the network head from eth_blockNumber when correctness matters.
• This reflects the node's own L2 import state on Arbitrum One; it does not tell you anything about Ethereum L1 finality or how far the rollup's batches have settled to L1. For settlement guarantees you must inspect L1 separately.
• The returned object's exact shape is client-specific — extra progress counters vary between Nitro builds and clients. Code that reads fields beyond startingBlock/currentBlock/highestBlock should handle missing keys gracefully.

Supported networks

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

See also

• eth_blockNumber
• eth_chainId
• net_peerCount

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_syncing","params":[]}'