> 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/flashblocks/base-flashblocks.md).

# Base Flashblocks

Flashblocks deliver \~200ms transaction preconfirmations on Base by streaming partial blocks before the next full block is sealed. Each 2-second Base block is divided into ten Flashblocks streamed at 200ms intervals, exposing preconfirmed state through the standard JSON-RPC `pending` block tag.

### Endpoints

| Transport | URL                                                       |
| --------- | --------------------------------------------------------- |
| HTTP      | `https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/` |
| WebSocket | `wss://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/`   |

{% hint style="info" %}
The `pending` tag works over HTTP. Flashblocks subscriptions require the WebSocket endpoint.
{% endhint %}

### Flashblocks-Aware Methods

<table data-search="false"><thead><tr><th>Method</th><th>Usage</th></tr></thead><tbody><tr><td><code>eth_getTransactionCount</code></td><td>Pass <code>"pending"</code> for a nonce that accounts for Flashblock transactions</td></tr><tr><td><code>eth_getStorageAt</code></td><td>Pass <code>"pending"</code> for storage at preconfirmed state</td></tr><tr><td><code>eth_getBalance</code></td><td>Pass <code>"pending"</code> for the balance at the latest Flashblock state</td></tr><tr><td><code>eth_getBlockByNumber</code></td><td>Pass <code>"pending"</code> to retrieve the current Flashblock</td></tr><tr><td><code>eth_getBlockReceipt</code></td><td>Pass <code>"pending"</code> to get receipts for all pre-confirmed transactions in the current Flashblock.</td></tr><tr><td><code>eth_getBlockTransactionCountByNumber</code></td><td>Pass <code>"pending"</code> to get the count of pre-confirmed transactions in the current Flashblock.</td></tr><tr><td><code>eth_estimateGas</code></td><td>Pass <code>"pending"</code> to estimate gas against preconfirmed state</td></tr><tr><td><code>eth_call</code></td><td>Pass <code>"pending"</code> to execute against preconfirmed state</td></tr><tr><td><code>eth_simulateV1</code></td><td>Simulates against the latest preconfirmed state</td></tr><tr><td><code>eth_getLogs</code></td><td>Pass <code>"fromBlock": "pending"</code> and <code>"toBlock": "pending"</code> to query logs from pre-confirmed transactions, updated every ~200ms.</td></tr><tr><td><code>eth_getCode</code></td><td>Pass <code>"pending"</code> for contract code at preconfirmed state</td></tr><tr><td><code>base_transactionStatus</code></td><td>Reports whether a transaction hash is present in the mempool</td></tr><tr><td><code>eth_subscribe</code></td><td>Opens a Flashblocks WebSocket subscription</td></tr><tr><td><code>eth_unsubscribe</code></td><td>Cancels an active Flashblocks subscription</td></tr></tbody></table>

### Example

The example below reads the `pending` balance of the Base WETH contract `0x4200000000000000000000000000000000000006`. Substitute any supported method and parameters; the `"pending"` tag is what selects Flashblock state.

{% tabs %}
{% tab title="cURL" %}
{% code overflow="wrap" %}

```bash
curl --location --request POST 'https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/' \
--header 'Content-Type: application/json' \
--data-raw '{
    "jsonrpc": "2.0",
    "method": "eth_getBalance",
    "params": ["0x4200000000000000000000000000000000000006", "pending"],
    "id": "getblock.io"
}'
```

{% endcode %}
{% endtab %}

{% tab title="Axios" %}
{% code title="example.js" %}

```javascript
const axios = require('axios');

const response = await axios.post('https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/', {
    jsonrpc: '2.0',
    method: 'eth_getBalance',
    params: ['0x4200000000000000000000000000000000000006', 'pending'],
    id: 'getblock.io'
}, {
    headers: { 'Content-Type': 'application/json' }
});

console.log(response.data.result);
```

{% endcode %}
{% endtab %}

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

```python
import requests

response = requests.post(
    'https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/',
    headers={'Content-Type': 'application/json'},
    json={
        'jsonrpc': '2.0',
        'method': 'eth_getBalance',
        'params': ['0x4200000000000000000000000000000000000006', 'pending'],
        'id': 'getblock.io'
    }
)

print(response.json())
```

{% endcode %}
{% endtab %}

{% tab title="Rust" %}
{% code title="example.rs" %}

```rust
use reqwest::Client;
use serde_json::{json, Value};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client = Client::new();

    let response = client
        .post("https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/")
        .header("Content-Type", "application/json")
        .json(&json!({
            "jsonrpc": "2.0",
            "method": "eth_getBalance",
            "params": ["0x4200000000000000000000000000000000000006", "pending"],
            "id": "getblock.io"
        }))
        .send()
        .await?
        .json::<Value>()
        .await?;

    println!("Result: {}", response["result"]);
    Ok(())
}
```

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

#### Response

```json
{
    "jsonrpc": "2.0",
    "id": "getblock.io",
    "result": "0x3bdf5275488a29a8a57c"
}
```

### Use Cases

* **Instant UI Feedback**: Update wallet and dApp interfaces the moment a transaction is preconfirmed, without waiting for a sealed block.
* **Responsive Swaps**: Surface preconfirmed swap results on decentralized exchanges with sub-second latency.
* **Onchain Gaming**: Reflect game state changes as soon as actions are included in a Flashblock.
* **Nonce Management**: Use `eth_getTransactionCount` with `pending` to avoid nonce collisions when submitting transactions in rapid succession.
* **Preconfirmed Receipts**: Poll `eth_getTransactionReceipt` on a 200ms interval to confirm inclusion at Flashblock cadence.