# generaltranslation: General Translation Core SDK: GTConstructorParams
URL: https://generaltranslation.com/en-US/docs/core/types/gt-constructor-params.mdx
---
title: GTConstructorParams
description: TypeScript interface for GT class constructor parameters
---

## Overview

`GTConstructorParams` defines configuration options for GT class initialization.

```typescript
interface GTConstructorParams {
  apiKey?: string;
  devApiKey?: string;
  sourceLocale?: string;
  targetLocale?: string;
  locales?: string[];
  projectId?: string;
  baseUrl?: string;
  customMapping?: CustomMapping;
}
```

All properties are optional. The constructor reads `GT_API_KEY`, `GT_DEV_API_KEY`, and `GT_PROJECT_ID` from environment variables if not provided.

## Properties

| Property | Type | Description |
|----------|------|-------------|
| `apiKey?` | `string` | Production API key |
| `devApiKey?` | `string` | Development API key |
| `sourceLocale?` | `string` | Default source locale |
| `targetLocale?` | `string` | Default target locale |
| `locales?` | `string[]` | Supported locale codes |
| `projectId?` | `string` | Project identifier |
| `baseUrl?` | `string` | Custom API endpoint |
| `customMapping?` | `CustomMapping` | Custom locale mappings |

## Examples

### Basic setup

```typescript copy
const gt = new GT({
  apiKey: 'your-api-key',
  sourceLocale: 'en',
  targetLocale: 'es',
  locales: ['en', 'es', 'fr']
});
```

### With environment variables

```typescript copy
const gt = new GT({
  sourceLocale: 'en',
  targetLocale: 'es'
});
// Uses GT_API_KEY and GT_PROJECT_ID from environment
```

## Related types

* [`CustomMapping`](/docs/core/types/custom-mapping) - Custom locale definitions