Cline

Cline is the open-source autonomous coding agent that gives AI the full power of a developer's toolkit inside VS Code — file editing, terminal access, browser control, and MCP integrations — while keeping you in control with a clear approval workflow. It's the transparent, customizable alternative to proprietary AI IDEs like Cursor and Windsurf.

Overview

Originally launched as "Claude Dev" in July 2024, Cline quickly became the most-starred AI coding extension for VS Code, driven by its unique approach: instead of hiding what the AI is doing, Cline shows you every action it plans to take and asks for your approval before executing. You see the exact file diffs, terminal commands, and browser actions before they happen.

In April 2026, Cline supports every major model through a bring-your-own-key model — Claude, GPT-4.1, Gemini, DeepSeek, and local models via Ollama. It is a first-class citizen in the Model Context Protocol (MCP) ecosystem, able to connect to any MCP server and use its tools as native capabilities.

Key Features

• Full Tool Suite: Cline can read/write any file, run any terminal command, control a Chromium browser via Puppeteer, and call external APIs — building a complete, real-world development workflow.
• Approval-First Transparency: Before taking any action (writing a file, running a command), Cline shows you exactly what it plans to do and waits for your "Approve" or "Reject."
• MCP Integration: Connects to any MCP server to extend its capabilities — databases, search engines, custom APIs, internal tools. The community maintains hundreds of pre-built MCP servers.
• Model-Agnostic Flexibility: Configure any model for any task. Use Claude for planning, DeepSeek for bulk code writing, and a local model for sensitive code — all within the same session.
• Context Window Management: Intelligently summarizes conversation history to prevent hitting model context limits on long tasks.
• Checkpoints: Creates git-based snapshots at key points so you can easily roll back to any earlier state.
• API Cost Tracking: Real-time display of API tokens consumed and cost per session, so you always know what you're spending.

How It Works

1. Task: You describe what you want built or fixed in the Cline sidebar chat.
2. Plan: Cline analyzes your codebase and formulates an action plan.
3. Approve: Each individual action (file edit, terminal command, browser navigation) is shown to you for approval.
4. Execute: Approved actions are executed and results are fed back to the model.
5. Iterate: Cline continues until the task is complete or you redirect it.

Technical Architecture:

• Platform: VS Code Extension (also works in VS Codium and compatible forks).
• Tool Execution: Node.js child processes for terminal, Puppeteer for browser.
• MCP Client: Full MCP client implementation for connecting to any MCP server.
• Git Integration: Checkpoint system using git stash for reversible state management.
• Model Integration: Via direct API calls to Anthropic, OpenAI, Google, DeepSeek, and Ollama.

Use Cases

End-to-End Feature Development

• "Build a REST API endpoint for user authentication with JWT tokens, including tests."
• "Create a responsive landing page for this product from the provided design spec."

Debugging with Real Context

• "The Docker container fails to start — here's the error log. Find and fix the issue."
• "Users are reporting slow page loads. Profile the API and optimize the top bottlenecks."

Browser-Assisted Development

• "Navigate to our staging site, fill in the registration form, and report if there are any UI errors."
• "Scrape the top 10 results from this search query and save them to a JSON file."

MCP-Powered Workflows

• Connect to a database MCP server and ask: "Show me all users registered in the last 7 days."
• Use a Slack MCP server to: "Post a summary of today's closed PRs to the #dev channel."

Getting Started

Step 1: Install Cline

1. Open VS Code.
2. Go to Extensions (Cmd+Shift+X).
3. Search for "Cline" and click Install.
4. The Cline icon will appear in the left sidebar.

Step 2: Add Your API Key

1. Click the Cline icon to open the sidebar.
2. Click the Settings (gear icon).
3. Choose your AI Provider (Anthropic is recommended for best results).
4. Paste your API key and select your preferred model.

Step 3: Start Your First Task

1. Open a project folder in VS Code.
2. Click the "+" button in the Cline sidebar to start a new task.
3. Describe your task clearly: "Add input validation to the /register endpoint in src/routes/auth.js."
4. Review Cline's plan and approve each step.

Step 4: Connect an MCP Server (Optional)

1. Open Cline settings and go to the "MCP Servers" tab.
2. Click "Add Server" and paste the MCP server config (JSON).
3. Cline will connect and list the server's available tools.
4. Reference the tools in your task: "Use the database tool to check the current schema."

Best Practices

• Be specific: "Add pagination to the GET /products endpoint with limit and offset query params" beats "improve the API."
• Use Checkpoints at the start of complex tasks so you can roll back easily.
• Monitor costs in the top-right of the Cline panel — DeepSeek V3 is 10x cheaper than Claude for bulk code writing.
• Use Auto-Approve for low-risk operations (reading files) and manual approval for writes and terminal commands.

Pricing & Access

• Cline Extension: Free and open-source (Apache 2.0). No subscription.
• API Costs (Bring Your Own Key):
  • Most cost-effective: DeepSeek V3 (~$0.27 per 1M input tokens).
  • Best quality: Claude Sonnet 4.5 (~$3 per 1M input tokens).
  • Free local option: Run ollama pull deepseek-coder-v2 and point Cline to your local Ollama instance.

Limitations

• VS Code Dependency: Primarily designed for VS Code — less useful outside the IDE environment.
• API Cost: Complex, multi-file tasks can consume significant tokens on premium models.
• Approval Overhead: The approval-first approach is safer but slower than fully autonomous modes in Cursor or Claude Code.
• Browser Control: Puppeteer-based browser automation can be brittle on complex web apps with heavy JavaScript.

Community & Support

• GitHub: github.com/cline/cline (35K+ stars)
• Discord: Official Cline Discord — very active community
• Documentation: docs.cline.bot
• MCP Servers: github.com/modelcontextprotocol/servers — community MCP server registry
• Reddit: r/cline

Related Tools

• Aider
• Cursor
• Claude Code
• Windsurf