Cline (formerly Claude Dev) began as a focused experiment: what would happen if you gave an AI model in VS Code the same capabilities a developer has — the ability to read files, write files, run terminal commands, and browse the web? The answer, after significant refinement, is Cline: a VS Code extension that turns your editor into a full agentic coding environment. With over 40,000 GitHub stars and a rapidly growing user base, Cline has become one of the most significant open-source contributions to AI-assisted development.
The fundamental design principle of Cline is transparent agency. Every action the agent takes — reading a file, writing changes, running a terminal command, making a browser request — requires explicit approval before execution. This is not just a safety feature; it is a learning and oversight mechanism. As you watch Cline navigate your codebase, read configuration files, trace function calls, and plan its approach, you develop a deep understanding of how an AI agent thinks about your code. The transparency teaches as much as it protects.
Installation through the VS Code marketplace takes thirty seconds. Cline adds a new panel to your VS Code sidebar with a simple chat interface. You configure an API key for your preferred model — Claude, GPT-4o, Gemini, or any OpenAI-compatible endpoint — and you are ready to work. Unlike standalone tools that require leaving your editor, Cline operates entirely within VS Code, maintaining your editor state, file context, and debugging session throughout an AI-assisted workflow.
Cline's tool suite gives it genuine agency. It can read any file in your workspace, write and modify files, create new files, execute terminal commands, and even open a browser to research documentation or APIs. This comprehensive toolset means Cline can handle tasks that require multiple types of actions — reading the current implementation, checking documentation for a library it needs to use, writing the new code, and running tests to verify correctness — all in a single, supervised workflow.
The auto-approve configuration is one of Cline's most thoughtful features. Rather than choosing between full autonomy and approving every action, you can configure granular approval requirements. Read operations can be auto-approved (they carry no risk). File writes can require approval (they are irreversible without git). Terminal commands can always require manual confirmation (they can have system-wide effects). This graduated trust model lets you tune the level of oversight to match the risk profile of each type of action.
Model flexibility is a core strength. Cline is model-agnostic and supports direct configuration of any API-compatible LLM. This means you can use Claude Opus for complex architectural tasks, Claude Sonnet for everyday coding, and a fast local model for quick edits — all within the same VS Code instance, changing based on the task at hand. For developers who have strong opinions about which models perform best for different types of work, this flexibility is essential.