Cline Review: The Open-Source Coding Agent That Lets You Pick Your Own Brain

The AI coding tool market has fractured into two camps. On one side, proprietary IDEs like Cursor and GitHub Copilot bundle everything into polished, subscription-gated packages. On the other, a growing contingent of developers wants the power of agentic coding without giving up their editor, their model choice, or their wallet. Cline sits squarely in that second camp - and with over 5 million installs and 58,000 GitHub stars, it has become the de facto open-source coding agent for VS Code.

After several weeks of intensive daily use across multiple projects and model providers, here is what Cline actually delivers, where it falls short, and who should care.

What Cline Actually Is

Cline is a VS Code extension - not a separate IDE, not a SaaS platform, not a CLI tool (though one exists now too). You install it from the marketplace, plug in an API key from whatever model provider you prefer, and you get an autonomous coding agent that lives in a sidebar panel inside your existing editor.

The distinction matters. Cursor requires you to switch to a VS Code fork. Copilot ties you to GitHub's ecosystem and pricing tiers. Cline works inside vanilla VS Code, with all your existing extensions, themes, and keybindings. If you have spent years customizing your VS Code setup, nothing changes except you now have an AI agent in the sidebar.

Under the hood, Cline is Apache 2.0 licensed, fully open-source, and funded by a recent $32 million raise from Emergence Capital and Pace Capital. The business model is straightforward: the extension is free, you bring your own API keys, and Cline sells managed inference credits at cost for teams who want centralized billing.

The Agentic Difference

What separates Cline from a chatbot bolted onto an editor is its ability to act. This is not autocomplete. Cline reads files, writes files, runs terminal commands, launches browsers, captures screenshots, monitors compiler errors, and iterates on its own work - all with your explicit approval at each step.

The workflow feels truly different from other coding assistants. You describe what you want in natural language - "add rate limiting middleware to the Express API" or "fix the failing test in auth.spec.ts" - and Cline creates a plan, reads the relevant files, makes changes across multiple files, runs the tests to verify, and presents you with diffs to approve or reject. The Plan/Act mode toggle lets you choose between reviewing a plan first or letting Cline dive straight into execution.

In practice, this works remarkably well for tasks that are well-defined but tedious. Setting up a new API endpoint with validation, error handling, and tests. Refactoring a module to use a different pattern. Debugging a failing CI pipeline by reading logs, identifying the issue, and applying the fix. These are the tasks where Cline earns its keep.

Where it gets shaky is on ambiguous, high-level architectural work. Tell Cline to "make the application more performant" and you will get a grab bag of changes that may or may not address actual bottlenecks. The agent works best with specific, concrete instructions - which, honestly, is true of every coding agent on the market right now.

Model Freedom Is the Killer Feature

This is where Cline truly differentiates itself. The extension supports Anthropic (Claude), OpenAI (GPT-4o, o1, o3), Google Gemini, AWS Bedrock, Azure OpenAI, GCP Vertex, Cerebras, Groq, and - critically - any OpenAI-compatible API endpoint, which means local models via Ollama or LM Studio.

In testing, we ran the same multi-file refactoring task across Claude Sonnet 4, GPT-4o, Gemini 2.0 Pro, and DeepSeek-R1 (via OpenRouter). Claude Sonnet 4 consistently produced the best results - more accurate code, better understanding of project conventions, fewer unnecessary changes. GPT-4o was close behind, occasionally edging ahead on straightforward tasks. Gemini 2.0 Pro was competent but slightly more verbose in its outputs. DeepSeek-R1 surprised with solid reasoning but occasionally produced formatting inconsistencies.

The point is not that one model is universally better. The point is that you can switch between them instantly, mid-conversation if you want. Running a quick prototype? Use a cheap model. Doing a critical refactor? Switch to Claude. Need to work offline? Spin up a local model through Ollama. No other mainstream coding agent offers this flexibility.

For teams weighing open-source against proprietary options, Cline represents the strongest argument for the open approach: you get the same agentic capabilities as closed competitors, without surrendering control over which models process your code.

Browser Automation and MCP

Two features push Cline beyond standard coding assistance. The first is browser automation - Cline can launch a headless browser, navigate to URLs, click elements, fill forms, and capture screenshots. This isn't just a demo gimmick. During testing, we used it to debug a CSS layout issue by having Cline launch the dev server, navigate to the broken page, capture a screenshot, identify the misaligned element, fix the CSS, and re-verify visually. The whole loop took about 90 seconds with one approval click.

The second is Model Context Protocol (MCP) support. MCP lets Cline connect to external tools and data sources - databases, APIs, documentation, deployment systems - through standardized server interfaces. Cline has a MCP marketplace with hundreds of pre-built servers, and it can even build new MCP servers for you on demand. Ask Cline to "add a tool that queries our Postgres database" and it'll scaffold a MCP server, configure the connection, and install it into the extension.

This extensibility is what makes Cline feel like a platform rather than a feature. As the MCP ecosystem grows, Cline's capabilities expand without any changes to the extension itself. It is a smart architectural bet.

The Cost Question

Here is the uncomfortable truth about Cline's "free" model: it's only free if you don't use it. Every API call to a model provider costs money, and agentic workflows consume clearly more tokens than simple autocomplete.

In our testing, a typical feature implementation session - adding a new API endpoint with tests and documentation - consumed roughly 80,000 to 150,000 tokens with Claude Sonnet 4. At current Anthropic pricing ($3/million input tokens, $15/million output tokens), that works out to roughly $0.80 to $2.00 per session. A full day of active development can easily hit $10 to $25.

Compare that to Cursor's flat $20/month or Copilot's $10/month, and the calculus gets interesting. Light users who run a few agent tasks per day will spend less than either subscription. Heavy users who let Cline handle complex multi-step workflows can blow past $50/month without trying hard. The cost tracker built into the extension helps - it shows token usage and estimated cost in real time for every task - but there is no spending cap or budget alert.

The Teams plan (free through Q1 2026, then $20/user/month) adds centralized billing, which helps organizations manage costs. But individual developers are on their own for budgeting.

Human-in-the-Loop Done Right

Cline's approval system is one of its best design decisions. Every file edit shows a full diff view. Every terminal command requires explicit approval. Every browser action is logged and reviewable. You are never in a position where the agent has made changes you didn't see.

This matters more than it might seem. The recent supply chain attack on Cline's own CLI package - where a compromised npm token was used to inject a postinstall script into [email protected] - is a stark reminder that AI developer tools operate in a high-trust environment. The VS Code extension was unaffected because it runs client-side and never touches npm publishing pipelines, but the incident highlights why Cline's zero-trust architecture and per-action approval system aren't just UX niceties. They're security necessities.

The flip side is that heavy approval fatigue is real. On a 20-step task, clicking "Approve" for every file write and terminal command gets tedious. Cline offers an auto-approve mode for terminal commands and file writes, but using it requires trusting the agent more than most developers should.

What Needs Work

Cline isn't perfect, and some of its limitations are fundamental rather than fixable with a patch.

Context window degradation is the biggest practical issue. Like all LLM-powered tools, Cline's accuracy drops as conversations grow longer. By turn 15 or 20, the model starts losing track of earlier context, repeating work, or making changes that conflict with earlier decisions. The solution is to start fresh conversations frequently, but this means losing continuity on complex tasks.

VS Code only (mostly). The extension recently added JetBrains support, which is welcome, but it remains mostly a VS Code tool. Vim, Emacs, and Sublime users are out of luck.

Cost unpredictability remains the elephant in the room. Without a flat-rate option, budgeting for Cline usage is guesswork. This is the single biggest barrier to enterprise adoption, despite the Teams and Enterprise plans attempting to address billing centralization.

Model quality variance means your experience depends heavily on which model you choose and how much you pay. The freedom to pick any model is a strength, but it also means Cline is only as good as the model behind it. Cheap models produce cheap results.

Strengths and Weaknesses

Strengths:

• True model agnosticism with support for every major provider and local models
• Full agentic capabilities - file editing, terminal execution, browser automation, MCP extensibility
• Stays inside VS Code - no editor switch, no workflow disruption
• Human-in-the-loop approval system is thoughtful and secure
• Open-source (Apache 2.0) with active community and $32M in funding
• Real-time cost tracking for every task

Weaknesses:

• API costs are unpredictable and can significantly exceed subscription competitors
• Context window degradation on long conversations degrades quality
• Approval fatigue on multi-step tasks slows down workflows
• No built-in spending caps or budget alerts
• Browser automation requires compatible model (works best with Claude)
• Quality is only as good as the model you choose to pay for

Verdict: 8.2/10

Cline is the best open-source coding agent available today, and it's the right tool for a specific kind of developer: someone who wants genuine agentic capabilities, values model freedom, prefers to stay in VS Code, and is comfortable managing their own API costs. If that describes you, Cline delivers. The Plan/Act workflow is polished, the MCP extensibility is forward-thinking, and the human-in-the-loop design strikes the right balance between autonomy and control.

It doesn't match Cursor's polish for pure inline coding assistance, and it can't compete with Copilot's ecosystem integration. But those tools ask you to give something up - your editor, your model choice, or your control over where your code gets sent. Cline asks you to give up nothing except a predictable monthly bill.

For an open-source project backed by a growing community and serious venture funding, that's a compelling trade.

Sources:

• Cline - Official Website
• Cline GitHub Repository
• Cline Documentation - What is Cline
• Cline MCP Overview
• Cline Pricing
• Cline Raises $32M Series A and Seed Funding
• Cline VS Code Marketplace
• Clinejection - Supply Chain Attack Disclosure