# Core Concepts

### Message Types

| Type | Description | Example |
|------|-------------|---------|
| **Text Message** | Simple text content | `"Hello world"` |
| **Image Message** | Text + image URL | `{ text: "Describe this", imageUrl: "..." }` |
| **System Prompt** | AI behavior/context | `"You are a helpful assistant"` |
| **Structured Message** | Multiple content parts | `[{ type: "text", text: "..." }, { type: "image_url", ... }]` |

### Provider Support

| Provider | Default Model | Base URL | Features |
|----------|---------------|----------|----------|
| **OpenRouter** | `mistralai/mistral-small-3.1-24b-instruct:free` | `https://openrouter.ai/api/v1` | Multiple models, free tier |
| **OpenAI** | `gpt-3.5-turbo` | `https://api.openai.com/v1` | GPT models, vision |
| **Anthropic** | `claude-3-haiku-20240307` | `https://api.anthropic.com/v1` | Claude models |
| **Custom** | User-defined | User-defined | Any OpenAI-compatible API |