# generaltranslation: General Translation Core SDK: setConfig
URL: https://generaltranslation.com/en-US/docs/core/class/set-config.mdx
---
title: setConfig
description: API reference for the GT setConfig method
---

## Overview

The `setConfig` method updates the configuration of an existing GT instance.
This allows you to modify API credentials, locales, and other settings after the instance has been created.

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

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


The `setConfig` method will validate all provided locale codes and merge with any existing configuration that was passed to the constructor.

---

## Reference

### Parameters

<TypeTable
  type={{
    "params": {
      type: 'GTConstructorParams',
      optional: false,
    }
  }}
/>

The `GTConstructorParams` object supports the same properties as the constructor:

| Property | Type | Optional | Description |
|----------|------|----------|-------------|
| `apiKey` | `string` | ✓ | Production API key for translation service |
| `devApiKey` | `string` | ✓ | Development API key |
| `projectId` | `string` | ✓ | Unique project identifier |
| `sourceLocale` | `string` | ✓ | Default source locale for translations |
| `targetLocale` | `string` | ✓ | Default target locale for translations |
| `locales` | `string[]` | ✓ | Array of supported locale codes |
| `baseUrl` | `string` | ✓ | Custom API base URL |
| `customMapping` | `CustomMapping` | ✓ | Custom locale code mappings |

### Returns

`void` - The method updates the instance configuration in-place.

---

## Example

In this example, we switch the target locale from Spanish to French.

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

// Switch to French
gt.setConfig({
  targetLocale: 'fr'
});
```

---

## Notes

- Configuration changes take effect immediately for subsequent method calls
- Environment variables are not re-read when calling `setConfig`
- Custom mappings completely replace existing mappings (not merged)
- Validation failures leave the instance configuration unchanged
- The method is synchronous and returns `void`

## Next steps

- **[Initialize with constructor](/docs/core/class/constructor)**
- **[Start translating content](/docs/core/class/methods/translation/translate)**
- **[Learn about GTConstructorParams](/docs/core/types/gt-constructor-params)**