Three AI Agents That Actually Write Code for You (and How to Use Them)

I got tired of copy-pasting snippets from ChatGPT. If you're still bouncing between your editor and a chat window, asking an LLM for code and then manually wiring it into your project, you're doing it the hard way.

In 2026, AI agents have matured into tools that read your entire codebase, propose multi-file changes, and execute commands on your behalf. They don't just autocomplete-they plan, edit, test, and iterate. I've been testing three agents that plug directly into real workflows: GitHub Copilot with GPT-5.6, Cursor, and Windsurf. Here's what they do and when to reach for each one.

What an AI agent actually means now

An agent isn't just a better autocomplete. It's a system that can:

• Read thousands of lines of your project to understand structure and conventions
• Generate a step-by-step plan for a feature or refactor
• Edit multiple files simultaneously
• Run tests, builds, or migrations and react to failures

Under the hood, they use frontier models like GPT-5.x, Claude Sonnet, and Gemini 2.0. The key difference from chat tools is execution: these agents live inside your editor or terminal and can act on your codebase without you shuttling text back and forth.

GitHub Copilot with GPT-5.6: the embedded option

GitHub Copilot shipped support for the GPT-5.6 family-Sol, Terra, and Luna-across VS Code, JetBrains, Xcode, the CLI, and GitHub.com itself. You pick the model variant in your editor's Copilot panel.

Sol is the heavyweight: use it for deep refactors where the agent needs to map dependencies across a monorepo and propose architectural changes. I used Sol to extract a shared package from a tangled TypeScript workspace. It read the import graph, suggested a migration plan, and generated a draft PR with file moves and updated tsconfig references.

Terra handles everyday coding-adding endpoints, fixing bugs, writing tests. Luna is fast and cheap for quick fixes.

You'll need a Copilot Business or Enterprise plan to access Sol and Terra in most IDEs; individual plans are rolling out. Setup is straightforward if you already have Copilot installed: just update your extension and select a model.

Cursor: agent workflows in a familiar editor

Cursor is a fork of VS Code with agentic features baked in. Cursor Tab gives you diff-style autocomplete that can rewrite entire functions. The chat and task panel lets you describe a feature, and Cursor will propose a plan, edit multiple files, and run commands.

I used Cursor to implement a REST endpoint in a Python/FastAPI service. I pasted an issue description into the task panel. Cursor scanned the project, suggested adding a handler in api/routes.py, a schema in models.py, and tests in tests/test_routes.py. It generated all three, ran pytest, caught a type mismatch, and fixed it in the next iteration.

Cursor supports Claude Sonnet and recent OpenAI models. It has a free tier with rate limits and a Pro plan for heavier use. The IDE layer is polished, so if you're comfortable in VS Code, the learning curve is minimal.

Windsurf: purpose-built for agent sessions

Windsurf is a new editor built from the ground up for agentic workflows. When you start a task, it generates a visible step-by-step plan, then calls a frontier model to execute each step-writing code, running terminal commands, reading compiler errors, and iterating.

I pointed Windsurf at a full-stack repo and asked it to add a dark-mode toggle to a React frontend, wire it to a user preference in the backend, and update docs. It laid out a plan (modify App.tsx, add a Zustand store, create a PUT endpoint, update README.md), executed each step, ran npm test, and surfaced the diffs for review.

Windsurf runs on Linux, Mac, and Windows. Setup is a fresh install (it's not a VS Code fork), but it imports your existing extensions and settings. The agent session UI is more explicit than Cursor's, which I found helpful for reviewing plans before committing.

Picking the right agent for the job

All three respect language conventions if your project has linters and formatters configured. Copilot integrates tightly with GitHub Actions and pull requests. Cursor feels more IDE-native. Windsurf makes the agent's reasoning visible, which I prefer when refactoring legacy code.

Keeping agents from breaking things

Letting an agent edit code and run commands can go sideways. Here's my checklist:

• Always work on a branch. Never point an agent at main.
• Review the plan before execution. All three tools show you what they're about to do-read it.
• Run tests after every agent session. If your suite is slow, run a subset.
• Audit terminal commands. Don't let an agent run rm -rf or install packages without confirmation.
• Use .gitignore and .cursorignore (or equivalent) to hide secrets. Agents shouldn't read .env files.

I treat agent output like a junior dev's PR: useful, but it needs a human review.

Try one this week

If you're already using Copilot, flip on Sol or Terra for your next refactor and compare it to your usual workflow. If you want more control, install Cursor and point it at a side project. If you like seeing the agent's reasoning, grab Windsurf and walk it through a feature from scratch.

Which of these have you tried, or are you sticking with plain autocomplete?