Beginner

Introduction to Gemini CLI

Discover Google's open-source AI coding agent for the terminal. Learn what Gemini CLI can do, how it works, and how it compares to other agentic coding tools.

What is Gemini CLI?

Gemini CLI is Google's open-source, agentic AI coding tool that runs directly in your terminal. It brings the power of Google's Gemini models to your command line, allowing you to interact with AI to read codebases, edit files, run commands, and perform complex development tasks - all through natural language.

Released as an open-source project, Gemini CLI is designed to be a developer's AI-powered pair programmer that lives in the terminal, similar to how Claude Code works for Anthropic's ecosystem.

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Open source: Gemini CLI is fully open-source, meaning you can inspect the code, contribute improvements, and understand exactly how it works. This transparency is a key differentiator from some closed-source alternatives.

Key Features

Gemini CLI is more than a simple chatbot - it is an agentic coding tool that can take actions in your development environment:

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Codebase Understanding

Gemini CLI reads and understands your entire codebase. Ask questions about architecture, find functions, trace dependencies, and get explanations of complex code.

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File Editing

Directly edit files in your project. Gemini CLI can create, modify, and refactor code across multiple files with your approval.

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Shell Commands

Execute shell commands to build, test, and run your project. Gemini CLI can chain commands together to complete complex tasks.

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Tool Use & Extensions

Extensible with custom tools and MCP (Model Context Protocol) servers. Connect to databases, APIs, and external services.

How It Works

Gemini CLI operates as an agentic loop in your terminal:

  1. You provide a task

    Type a natural language request describing what you want to accomplish, such as "Fix the bug in the login handler" or "Add unit tests for the user service."

  2. Gemini reads your codebase

    The agent examines relevant files in your project to understand the code structure, dependencies, and context needed to complete your task.

  3. Gemini plans and acts

    It creates a plan, then uses tools to edit files, run commands, search for information, and iterate until the task is complete.

  4. You review and approve

    Before making changes, Gemini CLI shows you what it plans to do. You approve, modify, or reject each action for full control.

Comparison with Claude Code

Both Gemini CLI and Claude Code are agentic AI coding tools for the terminal. Here is how they compare:

Feature Gemini CLI Claude Code
Developer Google Anthropic
Open Source Yes (Apache 2.0) No (proprietary)
AI Model Gemini 2.5 Pro / Flash Claude Sonnet / Opus
Context Window Up to 1M tokens Up to 200K tokens
Authentication Google account (free) Anthropic API key (paid)
Free Usage Generous free tier with Gemini Requires API credits
File Editing Yes, with approval Yes, with approval
Shell Commands Yes, sandboxed option Yes, with permission modes
MCP Support Yes Yes
Multimodal Yes (images, etc.) Yes (images)
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Key advantage: Gemini CLI's free tier with Google authentication makes it accessible to all developers without upfront API costs. Its open-source nature also means the community can extend and improve the tool.

What You Can Build

With Gemini CLI, you can accomplish tasks like:

  • Bug fixing: Describe a bug and let Gemini CLI trace the issue, find the root cause, and implement a fix
  • Feature development: Describe a feature in natural language and have Gemini CLI scaffold the implementation
  • Code review: Ask Gemini CLI to review your changes for bugs, performance issues, and best practices
  • Test writing: Generate comprehensive test suites for existing code
  • Refactoring: Restructure code with confidence while maintaining functionality
  • Documentation: Generate API docs, READMEs, and inline comments from your codebase

💡 Try It: Plan Your First Task

Think about a task in your current project that you would want an AI coding agent to help with. Write it down as a natural language instruction - this is exactly how you will interact with Gemini CLI.

You'll use this task to practice with Gemini CLI once you've completed the installation in the next lesson.

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