Cline (formerly Claude Dev) is an open-source VS Code extension that implements the agentic coding loop transparently. Every tool call the AI makes is visible in the sidebar — you can watch the agent read files, execute commands, edit code, and see the reasoning behind each action. This transparency makes Cline the best way to learn how agentic coding actually works.
Install as a VS Code extension, provide your own API key (Anthropic, OpenAI, OpenRouter, or local via Ollama), and start a task. Cline runs the standard agentic loop: read context, plan, execute tools, iterate until done. Unlike Cursor which runs on Cursor's servers, Cline runs locally in your VS Code — your code never leaves your machine except for the specific LLM calls. Open source means you can audit, fork, or extend it.
Cline itself is completely free and open source. You pay directly for LLM API usage (typically $1-10/day for active use depending on model choice). No subscription, no middleman, no data collection.
Open-source purists, privacy-conscious developers, students, and anyone who wants to understand how agentic IDEs work under the hood. Growing rapidly in 2026.