> 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/polkadot-dot/polkadot-json-rpc-api-relaychain/mmr_generateproof-polkadot.md).

# mmr\_generateProof - Polkadot

Example code for the mmr\_generateProof JSON RPC method. Complete guide on how to use mmr\_generateProof JSON RPC in GetBlock Web3 documentation.

This method generates an MMR proof for one or more block numbers, returning the leaves and the proof needed to verify them against the MMR root.

## Parameters

| Parameter            | Type    | Required | Description                                                       |
| -------------------- | ------- | -------- | ----------------------------------------------------------------- |
| blockNumbers         | array   | Yes      | Block numbers to prove                                            |
| bestKnownBlockNumber | integer | No       | Block number whose MMR state to prove against                     |
| at                   | string  | No       | Block hash to query at. Defaults to the latest block when omitted |

## Request

{% 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": "mmr_generateProof", "params": [[6754000]], "id": "getblock.io"}'
```

{% endcode %}
{% endtab %}

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

```javascript
const response = await fetch('https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({
        jsonrpc: '2.0',
        method: 'mmr_generateProof',
        params: [[6754000]],
        id: 'getblock.io'
    })
});

const data = await response.json();
console.log(data.result);
```

{% endcode %}
{% endtab %}

{% tab title="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': 'mmr_generateProof',
        'params': [[6754000]],
        'id': 'getblock.io'
    }
)

print(response.json()['result'])
```

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

## Response

```json
{
    "id": "getblock.io",
    "jsonrpc": "2.0",
    "result": {
        "blockHash": "0x255bc00927df8d33d561792635cbc6bde480a0a505eef5ff28630ece3fc15b32",
        "leaves": "0xc501...",
        "proof": "0x0401..."
    }
}
```

## Response Parameters

| Parameter | Type   | Description                             |
| --------- | ------ | --------------------------------------- |
| id        | string | Request identifier matching the request |
| jsonrpc   | string | JSON-RPC protocol version ("2.0")       |
| result    | object | MMR proof object                        |

### Result Object

| Field     | Type   | Description                           |
| --------- | ------ | ------------------------------------- |
| blockHash | string | Block the proof is generated at       |
| leaves    | string | SCALE-encoded MMR leaves, hex-encoded |
| proof     | string | SCALE-encoded MMR proof, hex-encoded  |

## Use Cases

* **Bridge Proofs**: Generate proofs for cross-chain verification
* **Historical Proofs**: Prove a past block belongs to the chain
* **Light Clients**: Provide verifiable history to light clients
* **Interoperability**: Feed BEEFY-based bridge relayers

## Error Handling

| Error Code | Message          | Description                                            |
| ---------- | ---------------- | ------------------------------------------------------ |
| -32602     | Invalid params   | A parameter is missing or has the wrong type or format |
| -32601     | Method not found | The method is not available on this endpoint           |
| -32603     | Internal error   | The node failed to process the request                 |

## Library Integration

The idiomatic way to call Polkadot RPC is the Polkadot.js API (`@polkadot/api`), which connects over WebSocket and exposes the method as `api.rpc.mmr.generateProof`.

{% code title="polkadot-js.js" %}

```javascript
import { ApiPromise, WsProvider } from '@polkadot/api';

const provider = new WsProvider('wss://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/');
const api = await ApiPromise.create({ provider });

const result = await api.rpc.mmr.generateProof([6754000]);
console.log(result.toHuman());
```

{% endcode %}