> ## 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.
</Note>

<Warning>
  This is an unstable RPC method that **Helius does not support**. This documentation is provided for reference only.
</Warning>

## 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.</Note>

## Authorizations

<ParamField query="api-key" type="string" required>
  Your Helius API key. You can get one for free in the [dashboard](https://dashboard.helius.dev/api-keys).
</ParamField>

## Body

<ParamField body="params" type="array" required>
  <Expandable title="properties" defaultOpen>
    <ParamField body="filter" type="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.
    </ParamField>

    <ParamField body="config" type="object">
      Configuration object containing the following fields:

      <ParamField body="commitment" type="string">
        The commitment level for the subscription. Can be `finalized`, `confirmed`, or `processed`.
      </ParamField>

      <ParamField body="encoding" type="string">
        Encoding format for the transaction data.
      </ParamField>

      <ParamField body="transactionDetails" type="string">
        Level of transaction detail to return.
      </ParamField>

      <ParamField body="maxSupportedTransactionVersion" type="number">
        The max transaction version to return in responses.
      </ParamField>

      <ParamField body="showRewards" type="boolean">
        Whether to show rewards in the response.
      </ParamField>
    </ParamField>
  </Expandable>
</ParamField>

## Response

<ResponseField name="result" type="integer">
  Subscription id (needed to unsubscribe)
</ResponseField>

## 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.

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

<ResponseExample>
  ```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
    }
  }
  ```
</ResponseExample>