> For the complete documentation index, see [llms.txt](https://docs.getblock.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.getblock.io/api-reference/cardano-ada/ogmios-websocket-api/nexttransaction-cardano.md).

# nextTransaction - Cardano

Example code for the nextTransaction WebSocket method. Complete guide on how to use nextTransaction WebSocket in GetBlock Web3 documentation.

This method returns the next transaction in the acquired mempool snapshot, allowing a client to list all pending transactions one at a time. This protocol requires a WebSocket connection.

## Parameters

| Parameter | Type   | Required | Description                                                    |
| --------- | ------ | -------- | -------------------------------------------------------------- |
| fields    | string | No       | Set to "all" to return full transaction objects instead of ids |

## Request

{% tabs %}
{% tab title="JavaScript" %}
{% code title="example.js" overflow="wrap" %}

```javascript
import WebSocket from 'ws';

const client = new WebSocket('wss://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/');

client.once('open', () => {
    client.send(JSON.stringify({"jsonrpc": "2.0", "method": "nextTransaction", "params": {"fields": "all"}, "id": "getblock.io"}));
});

client.on('message', (msg) => {
    console.log(JSON.parse(msg.toString()));
    client.close();
});
```

{% endcode %}
{% endtab %}

{% tab title="Python" %}
{% code title="example.py" %}

```python
import asyncio
import json
import websockets

async def main():
    async with websockets.connect('wss://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/') as ws:
        await ws.send(json.dumps({"jsonrpc": "2.0", "method": "nextTransaction", "params": {"fields": "all"}, "id": "getblock.io"}))
        print(json.loads(await ws.recv()))

asyncio.run(main())
```

{% endcode %}
{% endtab %}
{% endtabs %}

## Response

```json
{
    "jsonrpc": "2.0",
    "method": "nextTransaction",
    "result": {
        "transaction": {
            "id": "10b54fd708ab2e5703979b4ba27ca0339882abc2062e77fbe51e625203a49642"
        }
    },
    "id": "getblock.io"
}
```

## Response Parameters

| Field       | Type   | Description                                                          |
| ----------- | ------ | -------------------------------------------------------------------- |
| transaction | object | The next mempool transaction, or null when the snapshot is exhausted |

## Use Cases

* **Mempool Listing**: Enumerate all pending transactions in a snapshot
* **Payment Detection**: Detect an incoming transaction before confirmation
* **Fee Analysis**: Collect pending transactions for fee modeling
* **Monitoring**: Feed pending transactions into an alerting pipeline

## Error Handling

| Error Code | Message              | Description                                             |
| ---------- | -------------------- | ------------------------------------------------------- |
| -32602     | Invalid params       | The request is malformed for the current protocol state |
| 4000       | Must acquire mempool | A snapshot must be acquired before this request         |
| -32603     | Internal error       | The node failed to answer the mempool request           |