What is a terminal coding agent (Claude Code, Codex, Antigravity CLI, OpenCode, Aider)?

The terminal is the text window where you type commands to your computer instead of clicking. A terminal coding agent is a program you launch there, inside a project folder, that turns a plain-language request into real work: it reads the relevant files, proposes a plan, edits code, runs commands such as your tests, and tells you what it did. Because the terminal is where developers already run and test their code, an agent that lives there can do the whole loop itself.

This guide has covered what a coding agent is and how Codex and Claude Code compare. As of October 2026 the field is wider, and the main choices differ less in what they can do than in which models they use, how they bill, and how open they are.

The main terminal agents in October 2026

A few details help you place each one. Anthropic's documentation says Claude Code also runs in VS Code, JetBrains, a desktop app and the web, all sharing the same project settings, and reads a CLAUDE.md file (or an existing AGENTS.md) at the start of every session. OpenAI's Codex pricing page puts the CLI in ChatGPT Plus at $20 a month and notes that an API key gives CLI access without cloud features. Google introduced Antigravity CLI in May 2026 as the successor to Gemini CLI, keeping skills, hooks and subagents, and stopped serving Gemini CLI to its consumer plans on June 18, 2026. OpenCode, released under the MIT licence, runs in the terminal, as a desktop app or in an editor, and can sign in with an existing GitHub Copilot or ChatGPT subscription. Aider is the veteran of the group: lighter on agent features, and it commits every change to git so you can undo it easily.

A worked example: a first session

Here is what a first, careful session looks like with any of these tools. The commands below use Claude Code; the others are similar.

1. Open the terminal and move into a copy of your project, or a small test project. Make sure it is tracked with git, so every change can be undone.
2. Start the agent by typing its name, for example claude.
3. Ask it to look before it touches anything:

Read this project and explain in plain words what it does, how to run it
and how to run its tests. Don't change any files.

1. Give one small, checkable task: "Add a test for the date formatting function, run the tests and show me the result."
2. When it asks permission to edit a file or run a command, read what it wants to do and approve only what you understand.
3. When it finishes, look at the change with git diff and run the tests yourself.

Do you need to be a developer to use one?

No, but you need a few developer habits. Anthropic's installation guide is written so that someone who has never opened a terminal can follow it, and the desktop and web versions of Claude Code avoid the terminal entirely. People with no programming background use these agents to build personal tools, clean up spreadsheets or automate small tasks.

What you do need is the judgment that a developer brings. An agent in your terminal can run real commands on your real files. That is exactly what makes it useful, and also why the permission prompts matter. Before you rely on one, learn four things: how to open a terminal and move between folders; how git lets you see and undo changes; how to run your project's tests or at least start it and click through; and never to paste passwords or API keys into the conversation.

Start in a copy of a project, keep tasks small, and say "explain before you change" until you trust how the agent works. Read every permission request instead of approving by reflex. If your project handles other people's data or money, have someone who reads code review the result before it goes live. Used this way, a terminal agent is less a replacement for learning to code than a patient tutor that also does the typing.