# generaltranslation: General Translation Core SDK: isValidLocale
URL: https://generaltranslation.com/en-US/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 properly formatted and recognized 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',
    }
  }}
/>

### Parameters description

| Parameter | Description |
|-----------|-------------|
| `locale` | BCP-47 locale code to validate. If not provided, uses the instance's `targetLocale` |
| `customMapping` | Optional custom mapping to check for additional valid locales. If not provided, uses the instance'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 mapping locales always validate as true (bypass standard validation)
- Supports private-use language codes (qaa-qtz)
- Returns `false` for malformed or unrecognized locale codes

## Next steps

- **[Get locale properties with getLocaleProperties](/docs/core/class/methods/locales/get-locale-properties)**
- **[Determine 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 CustomMapping type](/docs/core/types/custom-mapping)**