# General Translation Platform: setConfig
URL: https://generaltranslation.com/en-GB/docs/platform/core/reference/gt-class/set-config.mdx
---

title: setConfig
description: Update the configuration of an existing GT instance. API Reference for setConfig.

---

Updates the configuration of an existing [GT](/docs/platform/core/reference/gt-class/constructor) instance. Use it to change API credentials, locales, and other settings after the instance has been created with General Translation.

## Overview [#overview]

Call `setConfig` to modify an instance in place. The new values merge with the configuration passed to the constructor and apply to every subsequent method call.

```typescript
const gt = new GT();

gt.setConfig({
  apiKey: 'your-new-api-key',
  projectId: 'your-project-id',
  sourceLocale: 'en',
  targetLocale: 'es',
});
```

Signature:

```typescript
setConfig(params: GTConstructorParams): void
```

*Note: `setConfig` is synchronous and returns `void`; it updates the instance in place.*

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

* **Locale standardisation, then validation.** Each provided locale code (`sourceLocale`, `targetLocale`, and every entry in `locales`) is first standardised to its canonical BCP 47 form, then validated. The **stored values are the standardised/normalised forms**, not the raw strings you passed. `setConfig` throws for invalid codes.
* **Custom mapping applies to `sourceLocale`/`targetLocale` but not to `locales`.** `sourceLocale` and `targetLocale` are validated **with** the `customMapping`, so a custom alias is accepted for them. Each entry in `locales` is validated **without** the mapping, so a `customMapping` alias is rejected if it appears inside `locales`.
* **Configuration merge.** New values merge with the configuration passed to the constructor. A `customMapping`, however, completely replaces any existing mapping rather than merging with it.
* **No environment re-read.** Environment variables (`GT_API_KEY`, `GT_DEV_API_KEY`, `GT_PROJECT_ID`) are not re-read when calling `setConfig`.
* **Not atomic.** If validation fails partway through (for example, on the second locale), earlier properties may already have been set.

## Parameters [#parameters]

`setConfig` accepts a required [`GTConstructorParams`](/docs/platform/core/reference/types/gt-constructor-params) object with the same properties as the [constructor](/docs/platform/core/reference/gt-class/constructor):

| Parameter                          | Description                                         | Type                                                                  | Optional | Default |
| ---------------------------------- | --------------------------------------------------- | --------------------------------------------------------------------- | -------- | ------- |
| [`apiKey`](#api-key)               | Production API key for the translation service.     | `string`                                                              | Yes      | —       |
| [`devApiKey`](#dev-api-key)        | Development API key.                                | `string`                                                              | Yes      | —       |
| [`projectId`](#project-id)         | Unique project identifier.                          | `string`                                                              | Yes      | —       |
| [`sourceLocale`](#source-locale)   | Default source locale for translations.             | `string`                                                              | Yes      | —       |
| [`targetLocale`](#target-locale)   | Default target locale for translations.             | `string`                                                              | Yes      | —       |
| [`locales`](#locales)              | Supported locale codes.                             | `string[]`                                                            | Yes      | —       |
| [`baseUrl`](#base-url)             | Custom API base URL.                                | `string`                                                              | Yes      | —       |
| [`customMapping`](#custom-mapping) | Custom locale code mappings and property overrides. | [`CustomMapping`](/docs/platform/core/reference/types/custom-mapping) | Yes      | —       |

The `params` object itself is required, although each of its properties is optional — pass only the settings you want to change.

### `apiKey` [#api-key]

**Type** `string` · **Optional**

Production API key for the translation service.

### `devApiKey` [#dev-api-key]

**Type** `string` · **Optional**

Development API key. Takes precedence over `apiKey` in development.

### `projectId` [#project-id]

**Type** `string` · **Optional**

Unique project identifier.

### `sourceLocale` [#source-locale]

**Type** `string` · **Optional**

Default source locale for translations. Standardised to its canonical form and stored in that normalised form, then validated **with** any `customMapping` (so a custom alias is accepted here).

### `targetLocale` [#target-locale]

**Type** `string` · **Optional**

Default target locale for translations. Standardised to its canonical form and stored in that normalised form, then validated against any `customMapping` (so a custom alias is accepted here).

### `locales` [#locales]

**Type** `string[]` · **Optional**

Array of supported locale codes. Each code is standardised to its canonical form and stored in that normalised form, then validated **without** the `customMapping` — so a `customMapping` alias that is valid for `sourceLocale`/`targetLocale` is rejected if it appears within `locales`.

### `baseUrl` [#base-url]

**Type** `string` · **Optional**

Custom API base URL.

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

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

Custom locale code mappings and property overrides. Unlike the other settings, a new `customMapping` completely replaces the existing mapping rather than merging with it.

## Returns [#returns]

**Type** `void`

The method updates the instance configuration in place and returns nothing.

## Examples [#examples]

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

// Switch the target locale from Spanish to French
gt.setConfig({
  targetLocale: 'fr',
});
```

## Notes [#notes]

* Configuration changes take effect immediately for subsequent method calls.
* Every locale code is standardised to its canonical form before being stored (the stored value is the normalised form), then validated.
* `sourceLocale` and `targetLocale` are validated with the `customMapping`; each entry in `locales` is validated without it.
* Environment variables are not re-read when calling `setConfig`.
* Custom mappings completely replace existing mappings (they are not merged).
* The update is **not atomic** — if validation fails partway through, earlier properties may already have been set.
* The method is synchronous and returns `void`.