Theia Coder Agent Mode: From AI Assistant to Autonomous Developer

Tired of micromanaging every code suggestion your AI coding assistant makes—manually reviewing each file and fixing its mistakes yourself?

There’s now a faster, more powerful alternative: Agent Mode in Theia Coder.

In the demo below, we show how Theia Coder, the AI coding assistant integrated in the AI-powered Theia IDE and built on Theia AI, evolves into a fully autonomous agent. With this new mode, it doesn’t just propose changes—it plans, writes, tests, iterates, and fixes code on its own.

🎥 Watch the full demo:

From Coder to Agent

Theia Coder already supported AI-assisted workflows via what we now call Edit Mode: a structured prompt-based interaction that gives you full control over which files are generated and when they’re committed.

But for certain tasks—especially greenfield development, complex testing, or multi-step workflows—that model hits its limits.

That’s where Agent Mode comes in.

This new mode gives the underlying LLM direct access to the workspace. It can:

• Write and modify files without user approval
• Compile and test the generated code
• Interpret results
• Fix its own errors
• Iterate until everything works

All of this happens autonomously, while still preserving the benefits of Theia IDE’s built-in mechanisms like context retrieval and change tracking.

Activating Agent Mode

Switching to Agent Mode is straightforward:

1. Navigate to the AI Configuration View and select Theia Coder as the active agent
2. Choose the agent-mode prompt
3. Optionally switch to a more powerful LLM like Sonnet-4, GPT-4.1 or Gemini-Pro
4. Enable notifications to get updates when long-running tasks complete

Once active, the agent behaves differently: it directly writes to the workspace, executes code, and even starts the app when done.

🧠 Tip: Agent Mode works best when paired with a clear, detailed prompt. Since it runs independently for 10–30 minutes, investing in better input yields significantly better results.
See our previous article and video about:

👉 How to write better prompts using Task Context

Behind the Scenes: A More Capable Prompt

One of the major differences in Agent Mode is the underlying prompt and the use of direct workspace tool functions—giving the LLM the power to apply changes immediately while preserving traceability via the Theia AI’s changeset feature.

If you’re building your own AI-powered tools using Theia AI, you can use and adapt these tool functions in your own agents too.

Get Started with Theia Coder Today!

🧪 Try Agent Mode in the AI-powered Theia IDE
📺 Watch the demo above to see it in action
📖 Learn how to write better prompts using Task Context
🚀 Build your own agents with Theia AI

At EclipseSource, we help teams create AI-native development environments, integrate custom agents, and bring autonomy and flexibility into their tools. Whether you’re building a coding IDE, a domain-specific engineering assistant, or just exploring AI-powered workflows—we’d love to hear from you.

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👉 Contact us to discuss your project