> ## Documentation Index
> Fetch the complete documentation index at: https://www.helius.dev/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# blockSubscribe

> Subscribe to receive notification anytime a new block is `confirmed` or `finalized`.

> [!NOTE]
>
> This subscription is considered **unstable** and is only available if the validator was started with the `--rpc-pubsub-enable-block-subscription` flag. The format of this subscription may change in the future.

> [!WARNING]
>
> This is an unstable RPC method that **Helius does not support**. This documentation is provided for reference only.

## Endpoints

Websockets are available on mainnet and devnet with the following URLs:

* **Mainnet** `wss://mainnet.helius-rpc.com/?api-key=<api-key>`
* **Devnet** `wss://devnet.helius-rpc.com/?api-key=<api-key>`

> [!NOTE]
>
> Websockets have a 10-minute inactivity timer; implementing health checks and sending pings every minute is heavily recommended to keep the websocket connection alive.

## Authorizations

**api-key** `string` *required*

Your Helius API key. You can get one for free in the [dashboard](https://dashboard.helius.dev/api-keys).

## Body

**params** `array` *required*

**properties**

**filter** `string | object` *required*

Filter criteria for the logs to receive results by account type; currently supported:

* `all` - include all transactions in block
* A JSON object with the following field:
  * `mentionsAccountOrProgram: <string>` - return only transactions that mention the provided public key (as base-58 encoded string). If no mentions in a given block, then no notification will be sent.

**config** `object`

Configuration object containing the following fields:

**commitment** `string`

The commitment level for the subscription. Can be `finalized`, `confirmed`, or `processed`.

**encoding** `string`

Encoding format for the transaction data.

**transactionDetails** `string`

Level of transaction detail to return.

**maxSupportedTransactionVersion** `number`

The max transaction version to return in responses. Set to `1` to receive legacy, v0, and v1 transactions.

**showRewards** `boolean`

Whether to show rewards in the response.

## Response

**result** `integer`

Subscription id (needed to unsubscribe)

## Notification Format

The notification will be an object with the following fields:

* `slot: <u64>` - The corresponding slot.
* `err: <object|null>` - Error if something went wrong publishing the notification otherwise null.
* `block: <object|null>` - A block object as seen in the `getBlock` RPC HTTP method.

```json Request theme={"system"}
{
  "jsonrpc": "2.0",
  "id": "1",
  "method": "blockSubscribe",
  "params": [
    {
      "mentionsAccountOrProgram": "LieKvPRE8XeX3Y2xVNHjKlpAScD12lYySBVQ4HqoJ5op"
    },
    {
      "commitment": "confirmed",
      "encoding": "base64",
      "showRewards": true,
      "transactionDetails": "full"
    }
  ]
}
```

```json Response theme={"system"}
{
  "jsonrpc": "2.0",
  "result": 0,
  "id": 1
}
```

```json Notification theme={"system"}
{
  "jsonrpc": "2.0",
  "method": "blockNotification",
  "params": {
    "result": {
      "context": {
        "slot": 112301554
      },
      "value": {
        "slot": 112301554,
        "block": {
          "previousBlockhash": "GJp125YAN4ufCSUvZJVdCyWQJ7RPWMmwxoyUQySydZA",
          "blockhash": "6ojMHjctdqfB55JDpEpqfHnP96fiaHEcvzEQ2NNcxzHP",
          "parentSlot": 112301553,
          "transactions": [
            {
              "transaction": [
                "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",
                "base64"
              ],
              "meta": {
                "err": null,
                "status": {
                  "Ok": null
                },
                "fee": 5000,
                "preBalances": [
                  1758510880, 2067120, 1566000, 1461600, 2039280, 2039280,
                  1900080, 1865280, 0, 3680844220, 2039280
                ],
                "postBalances": [
                  1758505880, 2067120, 1566000, 1461600, 2039280, 2039280,
                  1900080, 1865280, 0, 3680844220, 2039280
                ],
                "innerInstructions": [
                  {
                    "index": 0,
                    "instructions": [
                      {
                        "programIdIndex": 13,
                        "accounts": [1, 15, 3, 4, 2, 14],
                        "data": "21TeLgZXNbtHXVBzCaiRmH"
                      },
                      {
                        "programIdIndex": 14,
                        "accounts": [3, 4, 1],
                        "data": "6qfC8ic7Aq99"
                      }
                    ]
                  }
                ],
                "logMessages": [
                  "Program QMNeHCGYnLVDn1icRAfQZpjPLBNkfGbSKRB83G5d8KB invoke [1]",
                  "Program QMWoBmAyJLAsA1Lh9ugMTw2gciTihncciphzdNzdZYV invoke [2]"
                ],
                "preTokenBalances": [
                  {
                    "accountIndex": 4,
                    "mint": "iouQcQBAiEXe6cKLS85zmZxUqaCqBdeHFpqKoSz615u",
                    "uiTokenAmount": {
                      "uiAmount": null,
                      "decimals": 6,
                      "amount": "0",
                      "uiAmountString": "0"
                    },
                    "owner": "LieKvPRE8XeX3Y2xVNHjKlpAScD12lYySBVQ4HqoJ5op",
                    "programId": "TokenkegQfeZyiNwAJbNbGKPFXCWuBvf9Ss623VQ5DA"
                  }
                ],
                "postTokenBalances": [
                  {
                    "accountIndex": 4,
                    "mint": "iouQcQBAiEXe6cKLS85zmZxUqaCqBdeHFpqKoSz615u",
                    "uiTokenAmount": {
                      "uiAmount": null,
                      "decimals": 6,
                      "amount": "0",
                      "uiAmountString": "0"
                    },
                    "owner": "LieKvPRE8XeX3Y2xVNHjKlpAScD12lYySBVQ4HqoJ5op",
                    "programId": "TokenkegQfeZyiNwAJbNbGKPFXCWuBvf9Ss623VQ5DA"
                  }
                ],
                "rewards": []
              }
            }
          ],
          "blockTime": 1639926816,
          "blockHeight": 101210751
        },
        "err": null
      }
    },
    "subscription": 14
  }
}
```


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