What Is Aider? How to Collaborate with AI in the Terminal and What It Can Do [Latest 2026]

What you'll learn in this article

• What kind of tool Aider is
• How to do AI pair programming in the terminal
• What Aider can and can't do
• How much is free and what it actually costs
• Criteria for deciding which developers it's right for

What Is Aider?

Aider is a free AI pair programmer that runs in the terminal (the black screen where you type commands). It is offered as open-source software (meaning anyone can view its source code), and one of its defining features is that it isn't locked to any particular company. When you're writing code, it feels as though a talented senior engineer is sitting right next to you, with the AI providing support. It integrates deeply with Git (a tool that tracks the history of code changes), so changes written by the AI are properly recorded, making it safe to use even in team development. Another appeal is that it can be adopted regardless of which editor you use — VS Code, JetBrains, or anything else.

What Aider Can Do

Aider can make code changes spanning multiple files all at once. For example, if you say "I want to rename this function," it will automatically find every file where that function is used and fix them all. It supports a wide range of languages — over 100, including Python, JavaScript, TypeScript, Rust, and Go. Another major feature is the ability to choose whichever AI model you prefer, such as Claude 4.6, GPT-5, or Gemini 2.5 Pro. Every time code is changed, Aider automatically commits (saves the change) to Git, so it remains clear who changed what and when. You can work alongside AI on a broad range of tasks, from bug fixes and adding new features to cleaning up code (refactoring).

How to Use Aider

Getting started with Aider is very straightforward. First, type pip install aider-chat in your terminal to install it. Next, obtain an API key (think of it as a key that lets you use the service) from an AI service you want to use, such as OpenAI or Anthropic. Once you set that key as an environment variable, simply type aider inside your project folder to launch it. After it starts, you can make requests in natural language — like "Add a login feature" or "Fix this bug" — just as you would in a normal conversation. When Aider changes your code, it is automatically committed to Git, so you can check the history later with git log. If you don't like a particular change, reverting it with git revert is also easy.

Pros and Cons of Aider

On the pros side, the tool itself is completely free, and you can freely choose whichever AI model you like. Unlike Cursor or GitHub Copilot, there's no monthly fee — you only pay the API usage charges for what you use. It's said that a light task costs under ¥10 per session, and even heavy use amounts to only a few hundred yen per day. Because it runs in the terminal, it's also easy to use when working on remote servers or over SSH connections. On the cons side, if you're not comfortable with terminal operations, you may find it confusing at first. Obtaining an API key and configuring your environment are also required, which can feel like a bit of a hurdle for beginners. Compared to GUI tools (tools you can operate with a mouse), it falls short in terms of visual intuitiveness.

Who Aider Is Best For

Aider is ideal for developers who are comfortable working in the terminal and for those who want to use different AI models across multiple projects. It's a particularly great fit for backend engineers who frequently work on remote servers, and for those who favor editors like Vim or Emacs. It's also recommended for independent developers who want to avoid monthly subscription fees, and for freelancers who prefer to pay only for what they use. If you're doing team development on GitHub, having a clear history of AI-made changes makes code review much easier. Conversely, those who aren't comfortable with the terminal, or beginners who prefer intuitive mouse-driven operation, may be better served by integrated tools like Cursor or GitHub Copilot.

Summary

• Aider is a free, terminal-based AI pair programmer
• Supports over 100 languages and multiple AI models
• The tool itself is free; you only pay API usage fees
• Integrates with Git to automatically manage change history
• Can handle changes spanning multiple files in a single operation
• Particularly recommended for developers comfortable with terminal operations

Aider will be a powerful option for anyone who wants to harness the power of AI while maintaining full freedom in their development workflow.

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This article is a cross-post from AI Friends.