google-gemini-api

What this skill does

# Google Gemini API - Complete Guide

**Version**: Phase 2 Complete ✅
**Package**: @google/[email protected] (⚠️ NOT @google/generative-ai)
**Last Updated**: 2025-10-25

---

## ⚠️ CRITICAL SDK MIGRATION WARNING

**DEPRECATED SDK**: `@google/generative-ai` (sunset November 30, 2025)
**CURRENT SDK**: `@google/genai` v1.27+

**If you see code using `@google/generative-ai`, it's outdated!**

This skill uses the **correct current SDK** and provides a complete migration guide.

---

## Status

**✅ Phase 1 Complete**:
- ✅ Text Generation (basic + streaming)
- ✅ Multimodal Inputs (images, video, audio, PDFs)
- ✅ Function Calling (basic + parallel execution)
- ✅ System Instructions & Multi-turn Chat
- ✅ Thinking Mode Configuration
- ✅ Generation Parameters (temperature, top-p, top-k, stop sequences)
- ✅ Both Node.js SDK (@google/genai) and fetch approaches

**✅ Phase 2 Complete**:
- ✅ Context Caching (cost optimization with TTL-based caching)
- ✅ Code Execution (built-in Python interpreter and sandbox)
- ✅ Grounding with Google Search (real-time web information + citations)

**📦 Separate Skills**:
- **Embeddings**: See `google-gemini-embeddings` skill for text-embedding-004

---

## Table of Contents

**Phase 1 - Core Features**:
1. [Quick Start](#quick-start)
2. [Current Models (2025)](#current-models-2025)
3. [SDK vs Fetch Approaches](#sdk-vs-fetch-approaches)
4. [Text Generation](#text-generation)
5. [Streaming](#streaming)
6. [Multimodal Inputs](#multimodal-inputs)
7. [Function Calling](#function-calling)
8. [System Instructions](#system-instructions)
9. [Multi-turn Chat](#multi-turn-chat)
10. [Thinking Mode](#thinking-mode)
11. [Generation Configuration](#generation-configuration)

**Phase 2 - Advanced Features**:
12. [Context Caching](#context-caching)
13. [Code Execution](#code-execution)
14. [Grounding with Google Search](#grounding-with-google-search)

**Common Reference**:
15. [Error Handling](#error-handling)
16. [Rate Limits](#rate-limits)
17. [SDK Migration Guide](#sdk-migration-guide)
18. [Production Best Practices](#production-best-practices)

---

## Quick Start

### Installation

**CORRECT SDK:**
```bash
npm install @google/[email protected]
```

**❌ WRONG (DEPRECATED):**
```bash
npm install @google/generative-ai  # DO NOT USE!
```

### Environment Setup

```bash
export GEMINI_API_KEY="..."
```

Or create `.env` file:
```
GEMINI_API_KEY=...
```

### First Text Generation (Node.js SDK)

```typescript
import { GoogleGenAI } from '@google/genai';

const ai = new GoogleGenAI({ apiKey: process.env.GEMINI_API_KEY });

const response = await ai.models.generateContent({
  model: 'gemini-2.5-flash',
  contents: 'Explain quantum computing in simple terms'
});

console.log(response.text);
```

### First Text Generation (Fetch - Cloudflare Workers)

```typescript
const response = await fetch(
  `https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-flash:generateContent`,
  {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'x-goog-api-key': env.GEMINI_API_KEY,
    },
    body: JSON.stringify({
      contents: [{ parts: [{ text: 'Explain quantum computing in simple terms' }] }]
    }),
  }
);

const data = await response.json();
console.log(data.candidates[0].content.parts[0].text);
```

---

## Current Models (2025)

### Gemini 2.5 Series (General Availability)

#### gemini-2.5-pro
- **Context**: 1,048,576 input tokens / 65,536 output tokens
- **Description**: State-of-the-art thinking model for complex reasoning
- **Best for**: Code, math, STEM, complex problem-solving
- **Features**: Thinking mode (default on), function calling, multimodal, streaming
- **Knowledge cutoff**: January 2025

#### gemini-2.5-flash
- **Context**: 1,048,576 input tokens / 65,536 output tokens
- **Description**: Best price-performance workhorse model
- **Best for**: Large-scale processing, low-latency, high-volume, agentic use cases
- **Features**: Thinking mode (default on), function calling, multimodal, streaming
- **Knowledge cutoff**: January 2025

#### gemini-2.5-flash-lite
- **Context**: 1,048,576 input tokens / 65,536 output tokens
- **Description**: Cost-optimized, fastest 2.5 model
- **Best for**: High throughput, cost-sensitive applications
- **Features**: Thinking mode (default on), function calling, multimodal, streaming
- **Knowledge cutoff**: January 2025

### Model Feature Matrix

| Feature | Pro | Flash | Flash-Lite |
|---------|-----|-------|------------|
| Thinking Mode | ✅ Default ON | ✅ Default ON | ✅ Default ON |
| Function Calling | ✅ | ✅ | ✅ |
| Multimodal | ✅ | ✅ | ✅ |
| Streaming | ✅ | ✅ | ✅ |
| System Instructions | ✅ | ✅ | ✅ |
| Context Window | 1,048,576 in | 1,048,576 in | 1,048,576 in |
| Output Tokens | 65,536 max | 65,536 max | 65,536 max |

### ⚠️ Context Window Correction

**ACCURATE**: Gemini 2.5 models support **1,048,576 input tokens** (NOT 2M!)
**OUTDATED**: Only Gemini 1.5 Pro (previous generation) had 2M token context window

**Common mistake**: Claiming Gemini 2.5 has 2M tokens. It doesn't. This skill prevents this error.

---

## SDK vs Fetch Approaches

### Node.js SDK (@google/genai)

**Pros:**
- Type-safe with TypeScript
- Easier API (simpler syntax)
- Built-in chat helpers
- Automatic SSE parsing for streaming
- Better error handling

**Cons:**
- Requires Node.js or compatible runtime
- Larger bundle size
- May not work in all edge runtimes

**Use when:** Building Node.js apps, Next.js Server Actions/Components, or any environment with Node.js compatibility

### Fetch-based (Direct REST API)

**Pros:**
- Works in **any** JavaScript environment (Cloudflare Workers, Deno, Bun, browsers)
- Minimal dependencies
- Smaller bundle size
- Full control over requests

**Cons:**
- More verbose syntax
- Manual SSE parsing for streaming
- No built-in chat helpers
- Manual error handling

**Use when:** Deploying to Cloudflare Workers, browser clients, or lightweight edge runtimes

---

## Text Generation

### Basic Text Generation (SDK)

```typescript
import { GoogleGenAI } from '@google/genai';

const ai = new GoogleGenAI({ apiKey: process.env.GEMINI_API_KEY });

const response = await ai.models.generateContent({
  model: 'gemini-2.5-flash',
  contents: 'Write a haiku about artificial intelligence'
});

console.log(response.text);
```

### Basic Text Generation (Fetch)

```typescript
const response = await fetch(
  `https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-flash:generateContent`,
  {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'x-goog-api-key': env.GEMINI_API_KEY,
    },
    body: JSON.stringify({
      contents: [
        {
          parts: [
            { text: 'Write a haiku about artificial intelligence' }
          ]
        }
      ]
    }),
  }
);

const data = await response.json();
console.log(data.candidates[0].content.parts[0].text);
```

### Response Structure

```typescript
{
  text: string,                  // Convenience accessor for text content
  candidates: [
    {
      content: {
        parts: [
          { text: string }       // Generated text
        ],
        role: string             // "model"
      },
      finishReason: string,      // "STOP" | "MAX_TOKENS" | "SAFETY" | "OTHER"
      index: number
    }
  ],
  usageMetadata: {
    promptTokenCount: number,
    candidatesTokenCount: number,
    totalTokenCount: number
  }
}
```

---

## Streaming

### Streaming with SDK (Async Iteration)

```typescript
const response = await ai.models.generateContentStream({
  model: 'gemini-2.5-flash',
  contents: 'Write a 200-word story about time travel'
});

for await (const chunk of response) {
  process.stdout.write(chunk.text);
}
```

### Streaming with Fetch (SSE Parsing)

```typescript
const response = await fetch(
  `https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-flash:streamGenerateContent`,
  {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'x-goog-api-key': en