Cline is a VS Code extension that gives an AI model direct control over your editor: it can read and write files, run terminal commands, and browse the web for research, all using whichever model you connect with your own API key, whether that's Claude, GPT, Gemini, or something local. Every action goes through an approval step before it executes, which keeps a human in the loop even as the agent works somewhat autonomously.
Its Plan/Act workflow splits work into a planning phase, where the agent lays out what it intends to do, and an execution phase where it actually makes the changes, giving developers a chance to redirect before anything happens to their code. Because it's bring-your-own-key rather than a bundled subscription, cost scales directly with model usage instead of a flat monthly fee.
Cline has over 5 million installs and more than 58,000 GitHub stars, making it one of the most widely adopted open-source coding agents, especially among developers who want agentic behavior without being locked into a single vendor's model or pricing.