Cline, Roo Code, and the New Wave of Open-Source Coding Agents

For most of the last few years, the conversation about AI in your editor was a conversation about autocomplete. Tab to accept. Cycle through suggestions. Move on. That ceiling has lifted. A new wave of open-source projects now act on your codebase: they read files, edit multiple files in one task, run terminal commands, ask for approval before writing, and work through plans across many turns. They are not assistants in the old sense. They are agents.

This post looks at four open-source projects that sit at the front of that shift: Cline, Roo Code, Continue, and Aider. Each one approaches the agent loop a bit differently, and each one is worth understanding before you pick a default.

What makes a coding agent different from an assistant

A coding assistant predicts the next chunk of code based on the file you have open. A coding agent takes a goal, breaks it into steps, and acts. The shape of the loop is roughly:

1. Read enough of the project to ground the next decision.
2. Propose a change as a diff or a series of edits.
3. Optionally execute commands such as installing a package, running a test, or starting a dev server.
4. Read the output and decide whether the change worked or needs revision.
5. Repeat until the goal is hit or the user stops it.

The interesting questions across tools are: where does the user get to step in, what exactly can the agent touch, and how does it handle big projects without burning a million tokens.

If you are new to the broader space, our best AI coding assistants of 2026 post covers the wider landscape. This piece zooms in on the open-source agent slice.

Cline: the editor agent that wants approvals

Cline is a VS Code extension that runs as a chat panel next to your editor. The README describes it as an AI assistant that can use your CLI and editor, with explicit human approval baked into the workflow. When Cline wants to edit a file, it shows a diff. When it wants to run a terminal command, it asks. You can step through every action or let it run further.

A few things stand out:

• It uses VS Code's terminal integration to run shell commands and read the output back into context.
• It can monitor linter and compiler errors as it edits and try to fix them on its own loop.
• It supports browser automation through computer-use style tools to click, type, and capture screenshots, useful when the bug is visual.
• Context primitives like @file, @folder, @url, and @problems let you pull specific things into the conversation rather than dumping the whole repo.

Cline supports a wide list of providers including Anthropic, OpenAI, Google, OpenRouter, AWS Bedrock, Azure, GCP Vertex, Cerebras, Groq, and any OpenAI-compatible endpoint. It can also point at a local model through LM Studio or Ollama. You can read the source on GitHub.

Roo Code: a multi-mode fork in the same family

Roo Code is another VS Code extension that takes the same general shape as Cline but leans hard on explicit modes. The README ships five out of the box:

• Code Mode for everyday edits and file operations.
• Architect Mode for planning systems, specs, and migrations before any code is touched.
• Ask Mode for fast Q and A about a codebase.
• Debug Mode for tracing issues, adding logs, and isolating root causes.
• Custom Modes that teams can build for their own workflows.

Modes matter because the failure modes of an agent are different at different points of a task. Asking the same prompt to write a system spec is different from asking it to land a one-line bugfix. Splitting that into separate operating personalities, with their own tool permissions and prompts, tends to keep agents from sprinting off in the wrong direction.

Roo Code also exposes MCP server support so you can plug in extra tools, and supports a wide model lineup similar to Cline.

Continue: agents that ride your pull requests

Continue takes a different tack. Rather than only being an in-IDE chat partner, the current Continue platform leans into source-controlled AI checks that run against pull requests as GitHub status checks. Each agent is defined as a markdown file in a .continue/checks/ directory in your repository. The agent runs, looks at the diff, and either returns a green status or returns red with suggested fixes.

This pushes the agent into your CI loop instead of only your editor. It pairs well with the IDE extensions for VS Code and JetBrains, and the cn CLI gives you a portable runner. If your team already lives in pull requests and reviews, this is a model that meets you where you are.

Aider: the terminal pair programmer

Aider is the odd one out: it lives in your terminal, not your IDE. You launch it in a project, it builds a map of the codebase, and you talk to it. Edits are committed to git automatically with descriptive messages, which means undo is just git revert.

Some Aider details that matter in practice:

• It supports 100 plus programming languages.
• It can lint and run your tests, then react to failures.
• It works with watch mode so you can drop instructions as code comments and Aider will pick them up.
• It supports voice input and image context, so you can drop a screenshot of a broken UI and have it work from that.
• It runs against any major model including Claude, GPT, DeepSeek, and local models.

The repository is on GitHub. Aider's git-first workflow is the cleanest demonstration of the agent pattern: every action is committed, every state is reachable, and you trust your version control to be your safety net.

Choosing between them

There is no single right pick, but there are reasonable defaults:

• If you want a friendly in-IDE chat with explicit approvals on every edit and command, start with Cline.
• If you want richer mode-based control and team-defined custom modes, try Roo Code.
• If your workflow is pull-request first and you want AI checks instead of AI editing, look at Continue.
• If you live in tmux and trust git to be your seatbelt, Aider is hard to beat.

All four are open source, all four can be pointed at local models through Ollama or any OpenAI-compatible endpoint, and all four reward a careful read of their docs before you let them touch a real codebase.

Tools mentioned in this post

• Cline: VS Code extension that runs as an autonomous coding agent with explicit approvals.
• Roo Code: VS Code agent with five built-in modes and custom mode support.
• Continue: open-source platform for source-controlled AI checks and IDE assistance.
• Aider: terminal-first AI pair programmer with automatic git commits.