Google Gemini API

Google Gemini API - Complete Guide

Version: Phase 2 Complete ✅ Package: @google/genai@1.27.0 (⚠️ 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If you see code using @google/generative-ai, it's outdated!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
2. Current Models (2025)
3. SDK vs Fetch Approaches
4. Text Generation
5. Streaming
6. Multimodal Inputs
7. Function Calling
8. System Instructions
9. Multi-turn Chat
10. Thinking Mode
11. Generation Configuration

Phase 2 - Advanced Features: 12. Context Caching 13. Code Execution 14. Grounding with Google Search

Common Reference: 15. Error Handling 16. Rate Limits 17. SDK Migration Guide 18. Production Best Practices

Quick Start

Installation

CORRECT SDK:

npm install @google/genai@1.27.0

❌ WRONG (DEPRECATED):

npm install @google/generative-ai  # DO NOT USE!

Environment Setup

export GEMINI_API_KEY="..."

Or create .env file:

GEMINI_API_KEY=...

First Text Generation (Node.js SDK)

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)

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

⚠️ 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)

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)

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

{
  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)

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)

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': env.GEMINI_API_KEY,
    },
    body: JSON.stringify({
      contents: [{ parts: [{ text: 'Write a 200-word story about time travel' }] }]
    }),
  }
);

const reader = response.body.getReader();
const decoder = new TextDecoder();
let buffer = '';

while (true) {
  const { done, value } = await reader.read();
  if (done) break;

  buffer += decoder.decode(value, { stream: true });
  const lines = buffer.split('\n');
  buffer = lines.pop() || '';

  for (const line of lines) {
    if (line.trim() === '' || line.startsWith('data: [DONE]')) continue;
    if (!line.startsWith('data: ')) continue;

    try {
      const data = JSON.parse(line.slice(6));
      const text = data.candidates[0]?.content?.parts[0]?.text;
      if (text) {
        process.stdout.write(text);
      }
    } catch (e) {
      // Skip invalid JSON
    }
  }
}

Key Points:

• Use streamGenerateContent endpoint (not generateContent)
• Parse Server-Sent Events (SSE) format: data: {json}\n\n
• Handle incomplete chunks in buffer
• Skip empty lines and [DONE] markers

Multimodal Inputs

Gemini 2.5 models support text + images + video + audio + PDFs in the same request.

Images (Vision)

SDK Approach

import { GoogleGenAI } from '@google/genai';
import fs from 'fs';

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

// From file
const imageData = fs.readFileSync('/path/to/image.jpg');
const base64Image = imageData.toString('base64');

const response = await ai.models.generateContent({
  model: 'gemini-2.5-flash',
  contents: [
    {
      parts: [
        { text: 'What is in this image?' },
        {
          inlineData: {
            data: base64Image,
            mimeType: 'image/jpeg'
          }
        }
      ]
    }
  ]
});

console.log(response.text);

Fetch Approach

const imageData = fs.readFileSync('/path/to/image.jpg');
const base64Image = imageData.toString('base64');

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: 'What is in this image?' },
            {
              inlineData: {
                data: base64Image,
                mimeType: 'image/jpeg'
              }
            }
          ]
        }
      ]
    }),
  }
);

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

Supported Image Formats:

• JPEG (.jpg, .jpeg)
• PNG (.png)
• WebP (.webp)
• HEIC (.heic)
• HEIF (.heif)

Max Image Size: 20MB per image

Video

// Video must be < 2 minutes for inline data
const videoData = fs.readFileSync('/path/to/video.mp4');
const base64Video = videoData.toString('base64');

const response = await ai.models.generateContent({
  model: 'gemini-2.5-flash',
  contents: [
    {
      parts: [
        { text: 'Describe what happens in this video' },
        {
          inlineData: {
            data: base64Video,
            mimeType: 'video/mp4'
          }
        }
      ]
    }
  ]
});

console.log(response.text);

Supported Video Formats:

• MP4 (.mp4)
• MPEG (.mpeg)
• MOV (.mov)
• AVI (.avi)
• FLV (.flv)
• MPG (.mpg)
• WebM (.webm)
• WMV (.wmv)

Max Video Length (inline): 2 minutes Max Video Size: 2GB (use File API for larger files - Phase 2)

Audio

const audioData = fs.readFileSync('/path/to/audio.mp3');
const base64Audio = audioData.toString('base64');

const response = await ai.models.generateContent({
  model: 'gemini-2.5-flash',
  contents: [
    {
      parts: [
        { text: 'Transcribe and summarize this audio' },
        {
          inlineData: {
            data: base64Audio,
            mimeType: 'audio/mp3'
          }
        }
      ]
    }
  ]
});

console.log(response.text);

Supported Audio Formats:

• MP3 (.mp3)
• WAV (.wav)
• FLAC (.flac)
• AAC (.aac)
• OGG (.ogg)
• OPUS (.opus)

Max Audio Size: 20MB

PDFs

const pdfData = fs.readFileSync('/path/to/document.pdf');
const base64Pdf = pdfData.toString('base64');

const response = await ai.models.generateContent({
  model: 'gemini-2.5-flash',
  contents: [
    {
      parts: [
        { text: 'Summarize the key points in this PDF' },
        {
          inlineData: {
            data: base64Pdf,
            mimeType: 'application/pdf'
          }
        }
      ]
    }
  ]
});

console.log(response.text);

Max PDF Size: 30MB PDF Limitations: Text-based PDFs work best; scanned images may have lower accuracy

Multiple Inputs

You can combine multiple modalities in one request:

const response = await ai.models.generateContent({
  model: 'gemini-2.5-flash',
  contents: [
    {
      parts: [
        { text: 'Compare these two images and describe the differences:' },
        { inlineData: { data: base64Image1, mimeType: 'image/jpeg' } },
        { inlineData: { data: base64Image2, mimeType: 'image/jpeg' } }
      ]
    }
  ]
});

Function Calling

Gemini supports function calling (tool use) to connect models with external APIs and systems.

Basic Function Calling (SDK)

import { GoogleGenAI, FunctionCallingConfigMode } from '@google/genai';

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

// Define function declarations
const getCurrentWeather = {
  name: 'get_current_weather',
  description: 'Get the current weather for a location',
  parametersJsonSchema: {
    type: 'object',
    properties: {
      location: {
        type: 'string',
        description: 'City name, e.g. San Francisco'
      },
      unit: {
        type: 'string',
        enum: ['celsius', 'fahrenheit']
      }
    },
    required: ['location']
  }
};

// Make request with tools
const response = await ai.models.generateContent({
  model: 'gemini-2.5-flash',
  contents: 'What's the weather in Tokyo?',
  config: {
    tools: [
      { functionDeclarations: [getCurrentWeather] }
    ]
  }
});

// Check if model wants to call a function
const functionCall = response.candidates[0].content.parts[0].functionCall;

if (functionCall) {
  console.log('Function to call:', functionCall.name);
  console.log('Arguments:', functionCall.args);

  // Execute the function (your implementation)
  const weatherData = await fetchWeather(functionCall.args.location);

  // Send function result back to model
  const finalResponse = await ai.models.generateContent({
    model: 'gemini-2.5-flash',
    contents: [
      'What's the weather in Tokyo?',
      response.candidates[0].content, // Original assistant response with function call
      {
        parts: [
          {
            functionResponse: {
              name: functionCall.name,
              response: weatherData
            }
          }
        ]
      }
    ],
    config: {
      tools: [
        { functionDeclarations: [getCurrentWeather] }
      ]
    }
  });

  console.log(finalResponse.text);
}

Function Calling (Fetch)

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: 'What's the weather in Tokyo?' }] }
      ],
      tools: [
        {
          functionDeclarations: [
            {
              name: 'get_current_weather',
              description: 'Get the current weather for a location',
              parameters: {
                type: 'object',
                properties: {
                  location: {
                    type: 'string',
                    description: 'City name'
                  }
                },
                required: ['location']
              }
            }
          ]
        }
      ]
    }),
  }
);

const data = await response.json();
const functionCall = data.candidates[0]?.content?.parts[0]?.functionCall;

if (functionCall) {
  // Execute function and send result back (same flow as SDK)
}

Parallel Function Calling

Gemini can call multiple independent functions simultaneously:

const tools = [
  {
    functionDeclarations: [
      {
        name: 'get_weather',
        description: 'Get weather for a location',
        parametersJsonSchema: {
          type: 'object',
          properties: {
            location: { type: 'string' }
          },
          required: ['location']
        }
      },
      {
        name: 'get_population',
        description: 'Get population of a city',
        parametersJsonSchema: {
          type: 'object',
          properties: {
            city: { type: 'string' }
          },
          required: ['city']
        }
      }
    ]
  }
];

const response = await ai.models.generateContent({
  model: 'gemini-2.5-flash',
  contents: 'What is the weather and population of Tokyo?',
  config: { tools }
});

// Model may return MULTIPLE function calls in parallel
const functionCalls = response.candidates[0].content.parts.filter(
  part => part.functionCall
);

console.log(`Model wants to call ${functionCalls.length} functions in parallel`);

Function Calling Modes

import { FunctionCallingConfigMode } from '@google/genai';

const response = await ai.models.generateContent({
  model: 'gemini-2.5-flash',
  contents: 'What's the weather?',
  config: {
    tools: [{ functionDeclarations: [getCurrentWeather] }],
    toolConfig: {
      functionCallingConfig: {
        mode: FunctionCallingConfigMode.ANY, // Force function call
        // mode: FunctionCallingConfigMode.AUTO, // Model decides (default)
        // mode: FunctionCallingConfigMode.NONE, // Never call functions
        allowedFunctionNames: ['get_current_weather'] // Optional: restrict to specific functions
      }
    }
  }
});

Modes:

• AUTO (default): Model decides whether to call functions
• ANY: Force model to call at least one function
• NONE: Disable function calling for this request

System Instructions

System instructions guide the model's behavior and set context. They are separate from the conversation messages.

SDK Approach

const response = await ai.models.generateContent({
  model: 'gemini-2.5-flash',
  systemInstruction: 'You are a helpful AI assistant that always responds in the style of a pirate. Use nautical terminology and end sentences with "arrr".',
  contents: 'Explain what a database is'
});

console.log(response.text);
// Output: "Ahoy there! A database be like a treasure chest..."

Fetch Approach

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({
      systemInstruction: {
        parts: [
          { text: 'You are a helpful AI assistant that always responds in the style of a pirate.' }
        ]
      },
      contents: [
        { parts: [{ text: 'Explain what a database is' }] }
      ]
    }),
  }
);

Key Points:

• System instructions are NOT part of contents array
• They are set once at the top level of the request
• They persist for the entire conversation (when using multi-turn chat)
• They don't count as user or model messages

Multi-turn Chat

For conversations with history, use the SDK's chat helpers or manually manage conversation state.

SDK Chat Helpers (Recommended)

const chat = await ai.models.createChat({
  model: 'gemini-2.5-flash',
  systemInstruction: 'You are a helpful coding assistant.',
  history: [] // Start empty or with previous messages
});

// Send first message
const response1 = await chat.sendMessage('What is TypeScript?');
console.log('Assistant:', response1.text);

// Send follow-up (context is automatically maintained)
const response2 = await chat.sendMessage('How do I install it?');
console.log('Assistant:', response2.text);

// Get full chat history
const history = chat.getHistory();
console.log('Full conversation:', history);

Manual Chat Management (Fetch)

const conversationHistory = [];

// First turn
const response1 = 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: [
        {
          role: 'user',
          parts: [{ text: 'What is TypeScript?' }]
        }
      ]
    }),
  }
);

const data1 = await response1.json();
const assistantReply1 = data1.candidates[0].content.parts[0].text;

// Add to history
conversationHistory.push(
  { role: 'user', parts: [{ text: 'What is TypeScript?' }] },
  { role: 'model', parts: [{ text: assistantReply1 }] }
);

// Second turn (include full history)
const response2 = 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: [
        ...conversationHistory,
        { role: 'user', parts: [{ text: 'How do I install it?' }] }
      ]
    }),
  }
);

Message Roles:

• user: User messages
• model: Assistant responses

⚠️ Important: Chat helpers are SDK-only. With fetch, you must manually manage conversation history.

Thinking Mode

Gemini 2.5 models have thinking mode enabled by default for enhanced quality. You can configure the thinking budget.

Configure Thinking Budget (SDK)

const response = await ai.models.generateContent({
  model: 'gemini-2.5-flash',
  contents: 'Solve this complex math problem: ...',
  config: {
    thinkingConfig: {
      thinkingBudget: 8192 // Max tokens for thinking (default: model-dependent)
    }
  }
});

Configure Thinking Budget (Fetch)

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: 'Solve this complex math problem: ...' }] }],
      generationConfig: {
        thinkingConfig: {
          thinkingBudget: 8192
        }
      }
    }),
  }
);

Key Points:

• Thinking mode is always enabled on Gemini 2.5 models (cannot be disabled)
• Higher thinking budgets allow more internal reasoning (may increase latency)
• Default budget varies by model (usually sufficient for most tasks)
• Only increase budget for very complex reasoning tasks

Generation Configuration

Customize model behavior with generation parameters.

All Configuration Options (SDK)

const response = await ai.models.generateContent({
  model: 'gemini-2.5-flash',
  contents: 'Write a creative story',
  config: {
    temperature: 0.9,           // Randomness (0.0-2.0, default: 1.0)
    topP: 0.95,                 // Nucleus sampling (0.0-1.0)
    topK: 40,                   // Top-k sampling
    maxOutputTokens: 2048,      // Max tokens to generate
    stopSequences: ['END'],     // Stop generation if these appear
    responseMimeType: 'text/plain', // Or 'application/json' for JSON mode
    candidateCount: 1           // Number of response candidates (usually 1)
  }
});

All Configuration Options (Fetch)

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 creative story' }] }],
      generationConfig: {
        temperature: 0.9,
        topP: 0.95,
        topK: 40,
        maxOutputTokens: 2048,
        stopSequences: ['END'],
        responseMimeType: 'text/plain',
        candidateCount: 1
      }
    }),
  }
);

Parameter Guidelines

Tips:

• For factual tasks: Use low temperature (0.0-0.3)
• For creative tasks: Use high temperature (0.7-1.5)
• topP and topK both control randomness; use one or the other (not both)
• Always set maxOutputTokens to prevent excessive generation

Context Caching

Context caching allows you to cache frequently used content (like system instructions, large documents, or video files) to reduce costs by up to 90% and improve latency.

How It Works

1. Create a cache with your repeated content
2. Reference the cache in subsequent requests
3. Save tokens - cached tokens cost significantly less
4. TTL management - caches expire after specified time

Benefits

• Cost savings: Up to 90% reduction on cached tokens
• Reduced latency: Faster responses by reusing processed content
• Consistent context: Same large context across multiple requests

Cache Creation (SDK)

import { GoogleGenAI } from '@google/genai';
import fs from 'fs';

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

// Create a cache for a large document
const documentText = fs.readFileSync('./large-document.txt', 'utf-8');

const cache = await ai.caches.create({
  model: 'gemini-2.5-flash',
  config: {
    displayName: 'large-doc-cache', // Identifier for the cache
    systemInstruction: 'You are an expert at analyzing legal documents.',
    contents: documentText,
    ttl: '3600s', // Cache for 1 hour
  }
});

console.log('Cache created:', cache.name);
console.log('Expires at:', cache.expireTime);

Cache Creation (Fetch)

const response = await fetch(
  'https://generativelanguage.googleapis.com/v1beta/cachedContents',
  {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'x-goog-api-key': env.GEMINI_API_KEY,
    },
    body: JSON.stringify({
      model: 'models/gemini-2.5-flash',
      displayName: 'large-doc-cache',
      systemInstruction: {
        parts: [{ text: 'You are an expert at analyzing legal documents.' }]
      },
      contents: [
        { parts: [{ text: documentText }] }
      ],
      ttl: '3600s'
    }),
  }
);

const cache = await response.json();
console.log('Cache created:', cache.name);

Using a Cache (SDK)

// Generate content using the cache
const response = await ai.models.generateContent({
  model: cache.name, // Use cache name as model
  contents: 'Summarize the key points in the document'
});

console.log(response.text);

Using a Cache (Fetch)

const response = await fetch(
  `https://generativelanguage.googleapis.com/v1beta/${cache.name}:generateContent`,
  {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'x-goog-api-key': env.GEMINI_API_KEY,
    },
    body: JSON.stringify({
      contents: [
        { parts: [{ text: 'Summarize the key points in the document' }] }
      ]
    }),
  }
);

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

Update Cache TTL (SDK)

import { UpdateCachedContentConfig } from '@google/genai';

await ai.caches.update({
  name: cache.name,
  config: {
    ttl: '7200s' // Extend to 2 hours
  }
});

Update Cache with Expiration Time (SDK)

// Set specific expiration time (must be timezone-aware)
const in10Minutes = new Date(Date.now() + 10 * 60 * 1000);

await ai.caches.update({
  name: cache.name,
  config: {
    expireTime: in10Minutes
  }
});

List and Delete Caches (SDK)

// List all caches
const caches = await ai.caches.list();
for (const cache of caches) {
  console.log(cache.name, cache.displayName);
}

// Delete a specific cache
await ai.caches.delete({ name: cache.name });

Caching with Video Files

import { GoogleGenAI } from '@google/genai';
import fs from 'fs';

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

// Upload video file
const videoFile = await ai.files.upload({
  file: fs.createReadStream('./video.mp4')
});

// Wait for processing
while (videoFile.state.name === 'PROCESSING') {
  await new Promise(resolve => setTimeout(resolve, 2000));
  videoFile = await ai.files.get({ name: videoFile.name });
}

// Create cache with video
const cache = await ai.caches.create({
  model: 'gemini-2.5-flash',
  config: {
    displayName: 'video-analysis-cache',
    systemInstruction: 'You are an expert video analyzer.',
    contents: [videoFile],
    ttl: '300s' // 5 minutes
  }
});

// Use cache for multiple queries
const response1 = await ai.models.generateContent({
  model: cache.name,
  contents: 'What happens in the first minute?'
});

const response2 = await ai.models.generateContent({
  model: cache.name,
  contents: 'Describe the main characters'
});

Key Points

When to Use Caching:

• Large system instructions used repeatedly
• Long documents analyzed multiple times
• Video/audio files queried with different prompts
• Consistent context across conversation sessions

TTL Guidelines:

• Short sessions: 300s (5 min) to 3600s (1 hour)
• Long sessions: 3600s (1 hour) to 86400s (24 hours)
• Maximum: 7 days

Cost Savings:

• Cached input tokens: ~90% cheaper than regular tokens
• Output tokens: Same price (not cached)

Important:

• You must use explicit model version suffixes (e.g., gemini-2.5-flash-001, NOT just gemini-2.5-flash)
• Caches are automatically deleted after TTL expires
• Update TTL before expiration to extend cache lifetime

Code Execution

Gemini models can generate and execute Python code to solve problems requiring computation, data analysis, or visualization.

How It Works

1. Model generates executable Python code
2. Code runs in secure sandbox
3. Results are returned to the model
4. Model incorporates results into response

Supported Operations

• Mathematical calculations
• Data analysis and statistics
• File processing (CSV, JSON, etc.)
• Chart and graph generation
• Algorithm implementation
• Data transformations

Available Python Packages

Standard Library:

• math, statistics, random, datetime, json, csv, re
• collections, itertools, functools

Data Science:

• numpy, pandas, scipy

Visualization:

• matplotlib, seaborn

Note: Limited package availability compared to full Python environment

Basic Code Execution (SDK)

import { GoogleGenAI, Tool, ToolCodeExecution } 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: 'What is the sum of the first 50 prime numbers? Generate and run code for the calculation.',
  config: {
    tools: [{ codeExecution: {} }]
  }
});

// Parse response parts
for (const part of response.candidates[0].content.parts) {
  if (part.text) {
    console.log('Text:', part.text);
  }
  if (part.executableCode) {
    console.log('Generated Code:', part.executableCode.code);
  }
  if (part.codeExecutionResult) {
    console.log('Execution Output:', part.codeExecutionResult.output);
  }
}

Basic Code Execution (Fetch)

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({
      tools: [{ code_execution: {} }],
      contents: [
        {
          parts: [
            { text: 'What is the sum of the first 50 prime numbers? Generate and run code.' }
          ]
        }
      ]
    }),
  }
);

const data = await response.json();

for (const part of data.candidates[0].content.parts) {
  if (part.text) {
    console.log('Text:', part.text);
  }
  if (part.executableCode) {
    console.log('Code:', part.executableCode.code);
  }
  if (part.codeExecutionResult) {
    console.log('Result:', part.codeExecutionResult.output);
  }
}

Chat with Code Execution (SDK)

const chat = await ai.chats.create({
  model: 'gemini-2.5-flash',
  config: {
    tools: [{ codeExecution: {} }]
  }
});

let response = await chat.sendMessage('I have a math question for you.');
console.log(response.text);

response = await chat.sendMessage(
  'Calculate the Fibonacci sequence up to the 20th number and sum them.'
);

// Model will generate and execute code, then provide answer
for (const part of response.candidates[0].content.parts) {
  if (part.text) console.log(part.text);
  if (part.executableCode) console.log('Code:', part.executableCode.code);
  if (part.codeExecutionResult) console.log('Output:', part.codeExecutionResult.output);
}

Data Analysis Example

const response = await ai.models.generateContent({
  model: 'gemini-2.5-flash',
  contents: `
    Analyze this sales data and calculate:
    1. Total revenue
    2. Average sale price
    3. Best-selling month

    Data (CSV format):
    month,sales,revenue
    Jan,150,45000
    Feb,200,62000
    Mar,175,53000
    Apr,220,68000
  `,
  config: {
    tools: [{ codeExecution: {} }]
  }
});

// Model will generate pandas/numpy code to analyze data
for (const part of response.candidates[0].content.parts) {
  if (part.text) console.log(part.text);
  if (part.executableCode) console.log('Analysis Code:', part.executableCode.code);
  if (part.codeExecutionResult) console.log('Results:', part.codeExecutionResult.output);
}

Visualization Example

const response = await ai.models.generateContent({
  model: 'gemini-2.5-flash',
  contents: 'Create a bar chart showing the distribution of prime numbers under 100 by their last digit. Generate the chart and describe the pattern.',
  config: {
    tools: [{ codeExecution: {} }]
  }
});

// Model generates matplotlib code, executes it, and describes results
for (const part of response.candidates[0].content.parts) {
  if (part.text) console.log(part.text);
  if (part.executableCode) console.log('Chart Code:', part.executableCode.code);
  if (part.codeExecutionResult) {
    // Note: Chart image data would be in output
    console.log('Execution completed');
  }
}

Response Structure

{
  candidates: [
    {
      content: {
        parts: [
          { text: "I'll calculate that for you." },
          {
            executableCode: {
              language: "PYTHON",
              code: "def is_prime(n):\n  if n <= 1:\n    return False\n  ..."
            }
          },
          {
            codeExecutionResult: {
              outcome: "OUTCOME_OK", // or "OUTCOME_FAILED"
              output: "5117\n"
            }
          },
          { text: "The sum of the first 50 prime numbers is 5117." }
        ]
      }
    }
  ]
}

Error Handling

for (const part of response.candidates[0].content.parts) {
  if (part.codeExecutionResult) {
    if (part.codeExecutionResult.outcome === 'OUTCOME_FAILED') {
      console.error('Code execution failed:', part.codeExecutionResult.output);
    } else {
      console.log('Success:', part.codeExecutionResult.output);
    }
  }
}

Key Points

When to Use Code Execution:

• Complex mathematical calculations
• Data analysis and statistics
• Algorithm implementations
• File parsing and processing
• Chart generation
• Computational problems

Limitations:

• Sandbox environment (limited file system access)
• Limited Python package availability
• Execution timeout limits
• No network access from code
• No persistent state between executions

Best Practices:

• Specify what calculation or analysis you need clearly
• Request code generation explicitly ("Generate and run code...")
• Check outcome field for errors
• Use for deterministic computations, not for general programming

Important:

• Available on all Gemini 2.5 models (Pro, Flash, Flash-Lite)
• Code runs in isolated sandbox for security
• Supports Python with standard library and common data science packages

Grounding with Google Search

Grounding connects the model to real-time web information, reducing hallucinations and providing up-to-date, fact-checked responses with citations.

How It Works

1. Model determines if it needs current information
2. Automatically performs Google Search
3. Processes search results
4. Incorporates findings into response
5. Provides citations and source URLs

Benefits

• Real-time information: Access to current events and data
• Reduced hallucinations: Answers grounded in web sources
• Verifiable: Citations allow fact-checking
• Up-to-date: Not limited to model's training cutoff

Two Grounding APIs

1. Google Search (googleSearch) - Recommended for Gemini 2.5

const groundingTool = {
  googleSearch: {}
};

Features:

• Simple configuration
• Automatic search when needed
• Available on all Gemini 2.5 models

2. Google Search Retrieval (googleSearchRetrieval) - Legacy (Gemini 1.5)

const retrievalTool = {
  googleSearchRetrieval: {
    dynamicRetrievalConfig: {
      mode: 'MODE_DYNAMIC',
      dynamicThreshold: 0.7 // Only search if confidence < 70%
    }
  }
};

Features:

• Dynamic threshold control
• Used with Gemini 1.5 models
• More configuration options

Basic Grounding (SDK) - Gemini 2.5

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: 'Who won the euro 2024?',
  config: {
    tools: [{ googleSearch: {} }]
  }
});

console.log(response.text);

// Check if grounding was used
if (response.candidates[0].groundingMetadata) {
  console.log('Search was performed!');
  console.log('Sources:', response.candidates[0].groundingMetadata);
}

Basic Grounding (Fetch) - Gemini 2.5

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: 'Who won the euro 2024?' }] }
      ],
      tools: [
        { google_search: {} }
      ]
    }),
  }
);

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

if (data.candidates[0].groundingMetadata) {
  console.log('Grounding metadata:', data.candidates[0].groundingMetadata);
}

Dynamic Retrieval (SDK) - Gemini 1.5

import { GoogleGenAI, DynamicRetrievalConfigMode } from '@google/genai';

const ai = new GoogleGenAI({ apiKey: process.en

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