> 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/nervos-ckb/estimate_cycle-nervos.md).

# estimate\_cycle - Nervos

Returns the estimated CKB-VM cycles needed to execute a transaction's scripts. Like Ethereum's `eth_estimateGas` but for CKB-VM cycles instead of gas. The transaction does not have to be valid for execution at the moment of the call.

## Parameters

| Parameter | Type        | Required | Description                        |
| --------- | ----------- | -------- | ---------------------------------- |
| tx        | Transaction | Yes      | Transaction to estimate cycles for |

## Request Example

{% tabs %}
{% tab title="cURL" %}

```bash
curl --location --request POST 'https://go.getblock.io/<ACCESS-TOKEN>/' \
--header 'Content-Type: application/json' \
--data-raw '{
    "jsonrpc": "2.0",
    "method": "estimate_cycles",
    "params": [
        {
            "version": "0x0",
            "cell_deps": [],
            "header_deps": [],
            "inputs": [],
            "outputs": [],
            "outputs_data": [],
            "witnesses": []
        }
    ],
    "id": "getblock.io"
}'
```

{% endtab %}

{% tab title="JavaScript (Axios)" %}

```javascript
import axios from 'axios';

const data = JSON.stringify({
    "jsonrpc": "2.0",
    "method": "estimate_cycles",
    "params": [
        {
            "version": "0x0",
            "cell_deps": [],
            "header_deps": [],
            "inputs": [],
            "outputs": [],
            "outputs_data": [],
            "witnesses": []
        }
    ],
    "id": "getblock.io"
});

const config = {
    method: 'post',
    url: 'https://go.getblock.io/<ACCESS-TOKEN>/',
    headers: {
        'Content-Type': 'application/json'
    },
    data: data
};

axios(config)
    .then(response => console.log(JSON.stringify(response.data, null, 2)))
    .catch(error => console.log(error));
```

{% endtab %}

{% tab title="Python (Requests)" %}

```python
import requests
import json

url = "https://go.getblock.io/<ACCESS-TOKEN>/"

payload = json.dumps({
    "jsonrpc": "2.0",
    "method": "estimate_cycles",
    "params": [
        {
            "version": "0x0",
            "cell_deps": [],
            "header_deps": [],
            "inputs": [],
            "outputs": [],
            "outputs_data": [],
            "witnesses": []
        }
    ],
    "id": "getblock.io"
})

headers = {
    'Content-Type': 'application/json'
}

response = requests.post(url, headers=headers, data=payload)
print(response.text)
```

{% endtab %}

{% tab title="Rust (Reqwest)" %}

```rust
use reqwest::Client;
use serde_json::json;

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

    let payload = json!({
        "jsonrpc": "2.0",
        "method": "estimate_cycles",
        "params": [
                {
                        "version": "0x0",
                        "cell_deps": [],
                        "header_deps": [],
                        "inputs": [],
                        "outputs": [],
                        "outputs_data": [],
                        "witnesses": []
                }
        ],
        "id": "getblock.io"
});

    let response = client
        .post("https://go.getblock.io/<ACCESS-TOKEN>/")
        .header("Content-Type", "application/json")
        .json(&payload)
        .send()
        .await?;

    let result: serde_json::Value = response.json().await?;
    println!("{:#?}", result);

    Ok(())
}
```

{% endtab %}
{% endtabs %}

## Response Example

{% code overflow="wrap" %}

```json
{
    "jsonrpc": "2.0",
    "id": "getblock.io",
    "result": {
        "cycles": "0x3a980"
    }
}
```

{% endcode %}

## Response Parameters

| Field         | Type   | Description                            |
| ------------- | ------ | -------------------------------------- |
| result.cycles | Uint64 | Estimated CKB-VM cycles consumed (hex) |

## Use Cases

* Wallet pre-flight checks before broadcasting a transaction
* Computing transaction fees based on cycle count
* Detecting transactions that would exceed cycle limits

## Error Handling

| Status Code | Error Message                   | Cause                                                               |
| ----------- | ------------------------------- | ------------------------------------------------------------------- |
| 403         | Forbidden                       | Missing or invalid `<ACCESS-TOKEN>`                                 |
| -32602      | Invalid params                  | Request parameters are missing or malformed                         |
| -32601      | Method not found                | Method does not exist or is not enabled on this node                |
| -32603      | Internal error                  | Server-side error while processing the request                      |
| 429         | Too Many Requests               | Rate limit exceeded for your plan                                   |
| -32000      | Transaction failed verification | Scripts in the transaction would revert; estimation cannot complete |

## SDK Integration

{% tabs %}
{% tab title="@ckb-lumos/lumos" %}

```javascript
import { RPC } from '@ckb-lumos/rpc';

const rpc = new RPC('https://go.getblock.io/<ACCESS-TOKEN>/');

// Lumos provides typed methods on `rpc` (e.g. rpc.getTipHeader(), rpc.getBlock(hash)).
// For raw access to any CKB RPC method:
const result = await rpc.send('estimate_cycles', [{"version": "0x0", "cell_deps": [], "header_deps": [], "inputs": [], "outputs": [], "outputs_data": [], "witnesses": []}]);
console.log(result);
```

{% endtab %}

{% tab title="ckb-sdk-python / requests" %}

```python
# Using the official CKB SDK Python (ckb-sdk-python).
# For methods not yet wrapped, fall back to raw requests.
import requests

response = requests.post('https://go.getblock.io/<ACCESS-TOKEN>/', json={
    'jsonrpc': '2.0',
    'id': 'getblock.io',
    'method': 'estimate_cycles',
    'params': [{"version": "0x0", "cell_deps": [], "header_deps": [], "inputs": [], "outputs": [], "outputs_data": [], "witnesses": []}]
}})
print(response.json())
```

{% endtab %}
{% endtabs %}


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.getblock.io/api-reference/nervos-ckb/estimate_cycle-nervos.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.