# generaltranslation: General Translation Core SDK: isValidLocale
URL: https://generaltranslation.com/en-GB/docs/core/class/methods/locales/is-valid-locale.mdx
---
title: isValidLocale
description: API reference for the GT isValidLocale method
---

## Overview

The `isValidLocale` method validates whether a locale code is correctly formatted and recognised as a valid BCP-47 locale.
It checks locale structure, language recognition, and regional/script validity using the `Intl` APIs, with support for custom locale mappings.

***

## Reference

### Parameters

<TypeTable
  type={{
  "locale?": {
    type: 'string',
    optional: true,
    default: 'this.targetLocale',
  },
  "customMapping?": {
    type: 'CustomMapping',
    optional: true,
    default: 'this.customMapping',
  }
}}
/>

### Parameter descriptions

| Parameter       | Description                                                                                                             |
| --------------- | ----------------------------------------------------------------------------------------------------------------------- |
| `locale`        | BCP-47 locale code to validate. If not provided, uses the instance&#39;s `targetLocale`                                 |
| `customMapping` | Optional custom mapping to check for additional valid locales. If not provided, uses the instance&#39;s `customMapping` |

### Returns

`boolean` - `true` if the locale is valid, `false` otherwise

### Throws

* `Error` - If no locale is provided and the instance has no `targetLocale` configured

***

## Examples

```typescript
const gt = new GT({
  sourceLocale: 'en',
  targetLocale: 'es'
});

const isValid = gt.isValidLocale('en-US');
console.log(isValid); // true

const isInvalid = gt.isValidLocale('invalid-locale');
console.log(isInvalid); // false
```

***


## Notes

* Performs comprehensive BCP-47 locale validation using browser Intl APIs
* Custom-mapped locales always validate as true (bypassing standard validation)
* Supports private-use language codes (qaa-qtz)
* Returns `false` for malformed or unrecognised locale codes

## Next steps

* **[Get locale properties with getLocaleProperties](/docs/core/class/methods/locales/get-locale-properties)**
* **[Determine the best locale with determineLocale](/docs/core/class/methods/locales/determine-locale)**
* **[Get locale names with getLocaleName](/docs/core/class/methods/locales/get-locale-name)**
* **[Learn about the CustomMapping type](/docs/core/types/custom-mapping)**