# General Translation Platform: isValidLocale
URL: https://generaltranslation.com/en-GB/docs/platform/core/reference/utility-functions/locales/is-valid-locale.mdx
---

title: isValidLocale
description: Check whether a value is a valid locale code without a GT instance. API reference for isValidLocale.

---

[`isValidLocale`](/docs/platform/core/reference/gt-class-methods/locales/is-valid-locale) is a standalone utility function from General Translation's Core library that validates whether a string is a valid BCP-47 locale code. It performs format validation without requiring a GT instance.

## Overview [#overview]

Import `isValidLocale` directly from `generaltranslation` and call it with a locale code. It does not require an API key or a [GT](/docs/platform/core/reference/gt-class/constructor) instance. For the instance-based equivalent, use the [`isValidLocale`](/docs/platform/core/reference/gt-class-methods/locales/is-valid-locale) method on a [`GT`](/docs/platform/core/reference/gt-class/constructor) instance instead.

```typescript
import { isValidLocale } from 'generaltranslation';

console.log(isValidLocale('en-US')); // true
console.log(isValidLocale('invalid')); // false
```

Signature:

```typescript
isValidLocale(locale: string, customMapping?: CustomMapping): boolean
```

## How it works [#how-it-works]

* **Format validation.** Validates the BCP-47 locale code format. This is purely format validation — no network requests are made.
* **Custom mapping.** Works with custom locale mappings, so aliases defined in a [`customMapping`](/docs/platform/core/reference/types/custom-mapping) are considered valid.
* **Stateless.** Suitable for utility libraries and user input validation.

## Parameters [#parameters]

| Parameter                          | Description                                   | Type                                                                  | Optional | Default |
| ---------------------------------- | --------------------------------------------- | --------------------------------------------------------------------- | -------- | ------- |
| [`locale`](#locale)                | The value to validate.                        | `string`                                                              | No       | —       |
| [`customMapping`](#custom-mapping) | Custom mapping to consider during validation. | [`CustomMapping`](/docs/platform/core/reference/types/custom-mapping) | Yes      | —       |

### `locale` [#locale]

**Type** `string` · **Required**

The value to validate as a BCP-47 locale code.

### `customMapping` [#custom-mapping]

**Type** [`CustomMapping`](/docs/platform/core/reference/types/custom-mapping) · **Optional**

An optional custom mapping whose aliases are recognised as valid.

## Returns [#returns]

**Type** `boolean`

`true` if the locale code is valid, `false` otherwise.

## Examples [#examples]

```typescript
import { isValidLocale } from 'generaltranslation';

// Valid locale codes
console.log(isValidLocale('en-US')); // true
console.log(isValidLocale('zh-CN')); // true
console.log(isValidLocale('es')); // true

// Invalid locale codes
console.log(isValidLocale('invalid')); // false
console.log(isValidLocale('en_US')); // false (underscore instead of hyphen)
console.log(isValidLocale('')); // false
```

## Notes [#notes]

* Validates BCP-47 locale code format.
* Works with custom locale mappings.
* Essential for user input validation.
* No network requests — pure format validation.
* Stateless function suitable for utility libraries.