eth_newFilter

eth_newFilter creates a server-side log filter on Arbitrum One and returns a hex filter ID. You define which logs you care about — a block range, one or more contract addresses, and topic patterns — and then poll the ID with eth_getFilterChanges to fetch only the matching logs emitted since your last poll, without re-sending the filter each time. On Arbitrum One, the ETH-fee Optimistic Rollup running Nitro/ArbOS, this is the standard way to watch contract events such as ERC-20 transfers or DEX swaps over plain HTTP. The endpoint is https://arbitrum.therpc.io/YOUR_API_KEY (chain ID 42161, 0xa4b1).

Use cases

• Poll for new ERC-20 Transfer events on a regular interval without re-specifying the full filter each time; on Arbitrum One's sub-second blocks you can poll more frequently than the ~12-second cadence typical of Ethereum L1.
• Monitor a Uniswap or Camelot pair contract for Swap events in a long-running indexer process by keeping one filter alive and reading incremental changes.

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

Try it live in the Arbitrum One playground.

Errors & troubleshooting

Common pitfalls

• Filters are discarded after roughly five minutes of inactivity, so implement recreation logic for when eth_getFilterChanges returns a filter-not-found error.
• Server-side filter state is bound to the connection and lost on reconnect; always be prepared to recreate the filter from your stored block range and topics.
• For real-time event streaming on Arbitrum One, eth_subscribe over WebSocket is more efficient than repeatedly polling a filter, especially given the chain's fast sequencer blocks.

Supported networks

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

See also

• eth_getFilterChanges
• eth_getFilterLogs
• eth_uninstallFilter
• eth_getLogs

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_newFilter","params":[]}'