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# Schema

This is a configuration section of [Custom MT](/advanced/custom-mt.md). Use this configuration to declare variables that will be stored locally, such as API keys for Machine Translation services.

## Object Structure

* **type**: `string`
* **name**: `string`
* **default**: `string|number`
* **required**: `boolean`
* **message**: `string` - error message displayed when validation fails

```json
{
    "schema": [
        { "type": "string", "name": "api_key", "default": "", "required": true, "message": "Required an API Key" },
        { "type": "string", "name": "formality", "default": "default", "required": true },
        { "type": "number", "name": "preserve_formatting", "default": 0, "required": true },            
    ]
}
```