eth_subscribe

eth_subscribe opens a push-based subscription over a WebSocket connection to an Avalanche C-Chain node. Instead of repeatedly polling for new data, your client registers interest in a stream — new block headers, matching logs, pending transaction hashes, or sync status — and the node pushes eth_subscription notifications as events occur. On the C-Chain, where Snowman consensus delivers finality in roughly one to two seconds, this lets you react to confirmed AVAX activity almost as fast as it lands. Point your WebSocket client at https://avalanche.therpc.io/YOUR_API_KEY (chain ID 43114, 0xa86a) using the wss:// scheme, and you can drive event-driven applications without the latency and overhead of a polling loop.

Use cases

• Subscribe to newHeads to stream fresh C-Chain block headers into a real-time dashboard, updating chain height and gas readings every block without a single poll.
• Subscribe to logs with an address and topic filter to receive events from a contract — for example Trader Joe swaps or an Aave lending market — the moment they are mined.
• Subscribe to newPendingTransactions to watch AVAX-denominated transactions enter the C-Chain mempool, useful for tracking submissions before they finalize under Snowman consensus.

Parameters

Response

Example request

1curl https://avalanche.therpc.io/YOUR_API_KEY \
2  -X POST \
3  -H "Content-Type: application/json" \
4  -d '{
5    "jsonrpc": "2.0",
6    "method": "eth_subscribe",
7    "params": [
8        "newHeads",
9        {}
10      ],
11    "id": 1
12  }'

Try it live in the Avalanche playground.

Errors & troubleshooting

Common pitfalls

• eth_subscribe only works over a WebSocket connection. Calling it over plain HTTP against https://avalanche.therpc.io/YOUR_API_KEY returns a "notifications not supported" error — connect with the wss:// scheme instead.
• Notifications emitted while your socket is disconnected are gone for good. Build reconnect logic, and after reconnecting, backfill the gap with eth_getLogs over the missed C-Chain block range so you do not lose events.
• Log notifications can arrive with removed: true during a chain reorganization. Although the C-Chain's fast Snowman finality makes deep reorgs rare, your handler should still process removed events explicitly to keep downstream state consistent.

Supported networks

• Mainnet — Chain ID: 43114
• Fuji

See also

• eth_unsubscribe
• eth_newFilter
• eth_getLogs
• eth_getFilterChanges

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