# Luhn Checksum

The Luhn algorithm, also known as the modulus 10 or mod 10 algorithm, is a simple checksum formula used to validate a variety of identification numbers, such as credit card numbers, IMEI numbers and Canadian Social Insurance Numbers. Luhn Checksum lives in the **Hashing** category of the `fx` menu.

## Parameter

| Parameter | Type   | Required | Default | Description                                            |
| --------- | ------ | -------- | ------- | ------------------------------------------------------ |
| Input     | string | yes      | —       | Value to transform. Previous step output or a literal. |

`Input` is the primary value (previous step output or a literal).

## Returned value

| Type     | Description                                 |
| -------- | ------------------------------------------- |
| `string` | Result of the Luhn Checksum transformation. |

## Limitations

- Wrong key, algorithm options, or malformed input typically raises an evaluation error — fix Input or options before re-running.

## Example

<details>
<summary>Run Luhn Checksum</summary>

The Luhn algorithm, also known as the modulus 10 or mod 10 algorithm, is a simple checksum formula used to validate a variety of identification numbers, such as credit card numbers, IMEI numbers and Canadian Social Insurance Numbers. Adjust optional parameters when the defaults do not match your payload.

1. Set **Input** to the value to transform (previous step output or a literal).

2. Confirm **Output value** shows the transformed result.

</details>