Cline

What is Cline?

Cline (formerly known as Claude Dev) is an open-source AI coding agent extension for VS Code, available for free download on the VS Code Marketplace. It allows you to use an AI agent directly within VS Code—not just for code completion, but for true multi-step task execution: modifying files, running commands, viewing output, and acting based on the results.

It supports multiple AI models: Claude 3.5 Sonnet (most recommended), GPT-4o, DeepSeek, Gemini, and others. You use your own API key and pay only for what you actually use, with no subscription required for Cline itself.

Core Capabilities

File Editing

Cline can directly read and modify any file in your project. If you say in the chat, "Change this method in UserService to be asynchronous," it reads the file, understands the code, makes the modification, and presents a diff for your review, which you can then accept or reject.

Every file modification displays a complete diff, showing you exactly what was there before and what has changed now, rather than operating as a black box.

Terminal Command Execution

Cline can run commands in your terminal:

• Install dependencies (npm install xxx)
• Run tests (npm test)
• Start the development server
• Execute any command you instruct it to run

Before executing each command, Cline requests your confirmation (or you can set up auto-approval). This design ensures that the agent’s actions are controllable rather than fully autonomous.

Multi-step Task Execution

This is Cline’s core capability, distinguishing it from standard code completion tools. You give it a task:

"Add user authentication to this Next.js app using NextAuth.js, support Google OAuth, and use Prisma + PostgreSQL for the database."

Cline will:

1. Analyze the existing codebase structure
2. Plan the necessary steps
3. Install required packages
4. Create and modify necessary files
5. Automatically read error messages and fix them when errors occur

You watch the entire process from the sidelines; Cline tells you what it is doing at each step, and you can stop or intervene at any time.

Browser Control (Experimental Feature)

Cline has experimental browser control capabilities—it can open a browser, interact with web pages, and read page content. This enables tasks that require interaction with external services.

Bring Your Own API, Pay-as-you-go

Cline’s most unique business model: you connect your own API key and pay Anthropic, OpenAI, etc., based on actual usage. Cline itself is free. This means:

• Light usage costs may be lower than subscribing to Cursor Pro ($20/month)
• Heavy usage costs may exceed the subscription fee, as Claude 3.5 Sonnet’s API charges per token
• You have precise control over your usage, with no risk of "running out of quota"

In practice, a complex task (modifying hundreds to thousands of lines of code) typically consumes only a few cents to tens of cents in API fees.

Comparison with Cursor

This is the most common comparison, as both tools share significant functional overlap:

Cline’s Advantages:

• Fully Open Source: You can inspect the code yourself, providing peace of mind for users with security concerns.
• No Need to Change Editors: If you have deeply customized your VS Code environment, there is no need to migrate to Cursor.
• Pay-as-you-go API Costs: Lighter users may find this more cost-effective.
• More Flexible Model Selection: You can use DeepSeek (cheaper), Gemini, or any other supported model,not subject to Cursor’s model selection restrictions.

Cursor’s Advantages:

• More Complete IDE Experience: Tab-based code completion, codebase indexing, and a more mature UI.
• Predictable Fixed Monthly Fee: Avoids unexpected API bills from large tasks.
• Larger Ecosystem: More tutorials and community support.

Who Should Use Cline?

VS Code Power Users: If you have configured VS Code to your liking and don’t want to switch IDEs but desire Cursor-level AI agent capabilities, Cline is the best choice.

Developers Preferring Open Source: Those who do not wish to use closed-source tools for code or have concerns about sending company code to third-party servers. Since Cline is open source, you can audit the code yourself.

Cost-Conscious Developers: If your usage frequency is low (a few times a week rather than heavy daily use), paying per API call may be cheaper than Cursor’s monthly fee.

Developers Wanting Specific APIs: For example, if you have a corporate Azure OpenAI account or want to save money using DeepSeek, Cline’s model flexibility is an advantage.

Users Wanting to Try AI Agent Coding: Since Cline is completely free (you only pay API fees), it is one of the lowest-cost ways to try out the AI agent coding experience.

Installation and Configuration

1. Search for "Cline" in the VS Code Marketplace and install it.
2. Open the Cline panel in the sidebar.
3. Enter your API key (Claude/OpenAI/etc.).
4. Start using it.

The entire configuration process takes no more than 5 minutes, which is the smoothest aspect compared to Cursor—no need to install new software or import configurations.

Usage Tips

Prioritize Claude 3.5 Sonnet. Although Cline supports many models, Claude 3.5 Sonnet performs significantly better in code understanding and multi-step task execution than other models, making it the recommended choice for most developers.

Set Reasonable Auto-Approval Rules. Each of Cline’s actions can be configured to require manual confirmation. It is advisable to keep manual review for file writes and command executions, while auto-approving file read operations. This balances security with convenience, avoiding frequent clicks for confirmation.

Provide Sufficient Context for Tasks. "Fix this bug" is too vague; "After user login, the redirect goes to /dashboard, but now it jumps to 404. I suspect a routing configuration issue; the specific code is in app/auth/callback/route.ts"—such detailed descriptions allow Cline to address the problem more directly.

Monitor API Costs. Complex tasks consume many tokens. Cline’s interface displays the consumption for the current session, so check it regularly to avoid unexpected bills.

Cline represents the open-source direction of AI coding tools. For developers who wish to maintain their VS Code workflow or have customized needs for AI coding tools, it is the most worthy option to seriously evaluate alongside Cursor and GitHub Copilot.