> For the complete documentation index, see [llms.txt](https://svpchain.gitbook.io/svpchain-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://svpchain.gitbook.io/svpchain-docs/build/websocket.md).
# WebSocket
WebSocket subscriptions — newHeads, logs, and reconnect strategy.
The WebSocket endpoint serves the standard `eth_subscribe` interface — same as on Ethereum. Use it for realtime feeds of new blocks and logs. For one-shot reads, prefer [JSON-RPC](/svpchain-docs/build/json-rpc.md) over HTTP.
* **Testnet:** `wss://svp-dataseeds-testnet.svpchain.org/ws`
* **Mainnet:** `wss://svp-dataseeds.svpchain.org/ws`
* Alternates: [Networks](/svpchain-docs/chain/networks.md).
### Subscriptions
| Subscription | What it streams |
| ------------------------ | -------------------------------------------------------------------- |
| `newHeads` | Block headers as they are committed (\~1/sec). |
| `logs` | Event logs matching the given filter (`address`, `topics`). |
| `newPendingTransactions` | Tx hashes entering the mempool. **Best-effort** on public endpoints. |
### Examples
#### Subscribe to new heads
```sh
echo '{"jsonrpc":"2.0","id":1,"method":"eth_subscribe","params":["newHeads"]}' \
| websocat wss://svp-dataseeds-testnet.svpchain.org/ws
```
The first response gives you a subscription ID; every subsequent message is a new block header.
#### Subscribe to logs from a contract
```sh
echo '{
"jsonrpc":"2.0","id":1,"method":"eth_subscribe",
"params":["logs",{
"address":"0xYourContract",
"topics":["0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef"]
}]
}' | websocat wss://svp-dataseeds-testnet.svpchain.org/ws
```
The `topics[0]` above is `keccak256("Transfer(address,address,uint256)")`.
#### Viem (TypeScript)
```ts
import { createPublicClient, webSocket, parseAbiItem } from "viem";
const client = createPublicClient({
transport: webSocket("wss://svp-dataseeds-testnet.svpchain.org/ws"),
});
client.watchBlockNumber({ onBlockNumber: (n) => console.log("head", n) });
client.watchEvent({
address: "0xYourContract",
event: parseAbiItem(
"event Transfer(address indexed from, address indexed to, uint256 value)"
),
onLogs: (logs) => console.log(logs),
});
```
### Recommended pattern
1. **Persist a cursor.** Save the last fully-processed block number to durable storage.
2. **Subscribe.** Open `newHeads` (or `logs`) and process events as they arrive.
3. **Confirm via JSON-RPC.** For each event, use HTTP RPC (`eth_getBlockByNumber`, `eth_getLogs`) as the canonical source — WS is a notification stream, not a database.
4. **Backfill on reconnect.** When the socket drops, read the cursor, call `eth_getLogs(cursor+1, currentHead)`, then resume.
### Reconnect strategy
* Use exponential backoff with a cap (e.g. 250ms → 8s).
* On any error or close event, reset and reconnect.
* Don't trust the socket-level "still alive" signal — also alert if the cursor stops advancing for more than a few seconds while the chain is producing blocks.
### SVPChain-specific notes
* **No reorgs.** Every committed block is final. You don't need a confirmation buffer or "unwind on reorg" code path.
* **CLOB events** are not in `eth_subscribe("logs", ...)`. To stream order-book activity, subscribe to **CometBFT** block events on the Cosmos surface. Endpoint and event schema: TODO.
* **`newPendingTransactions`** is best-effort on public endpoints — run your own node for a reliable mempool feed.
### Next steps
---
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