GenAI-based development platform - part 3: Announcing Isolarium, three flavors of secure sandboxes for GenAI-based coding agents

I’m pleased to announce that I’ve open-sourced Isolarium , a companion project to Idea to Code workflow that provides secure sandboxes for running GenAI-based coding agents like Claude Code. This article is part of a series about the GenAI-based development platform (a.k.a. harness) that I’ve been developing to make GenAI-based coding agents like Claude Code more productive, more secure and less frustrating. The complete list of articles in the series is as follows: Part 0 - My GenAI development workflow: Idea to Code Part 1 - Guardrails for GenAI coding agents Part 2 - How Idea to Code turns an idea into working, tested software Part 3 - Announcing Isolarium, three flavors of secure sandboxes for GenAI-based coding agents Part 4 - The coding agent sandwich pattern In this article, I first describe the risks of running coding agents on a developer workstation and why secure sandboxes are necessary. I then briefly describe Isolarium and the three flavors of sandboxes that it offers. Let’s start by looking at the motivation for Isolarium. Why coding agents need secure sandboxes There are three reasons why coding agents need secure sandboxes: Coding agents are vulnerable to attacks that can compromise the developer’s machine Container-based testing libraries such as Testcontainers introduce additional risks Even well-intentioned coding agents can cause damage Let’s look at each one. Coding agent security risks Coding agent security risks have been on my mind ever since I watched the excellent and deeply disturbing presentation Agentic ProbLLMs: Exploiting AI Computer-Use and Coding Agents by AI researcher Johann Rehberger . His The Month of AI Bugs series - one post per day for the month of August 2025 - shows the risks that we face when we run coding agents. Coding agent security risks include: Exfiltration of developer credentials (SSH keys, GitHub tokens, cloud credentials) Leakage of sensitive local files from the developer workstation Unauthorized access to other repositories or organization resources Execution of malicious commands on the developer’s machine Malicious or unsafe dependency installation affecting the host environment Persistence of compromise on the developer machine after an agent session ends Container-based testing libraries introduce additional risks Testing technologies such as the incredibly useful Testcontainers library that allow tests to run arbitrary Docker containers introduce additional risks since they can be used to run malicious containers that attack the host machine. Even well-intentioned coding agents can cause damage There’s also the risk of a well-intentioned coding agent causing damage by making unintended changes to the developer’s machine or code repository. Coding agents, for example, attempt to run arbitrary Bash commands, or write code that runs Bash commands. Secure sandboxes for GenAI-based coding agents Isolarium is a command line tool intended to address these problems. It runs coding agents in a secure, isolated and disposable environment. For example, to run Claude Code: $ cd my-project $ isolarium run –create – claude -p … This command creates an isolated environment for the coding agent to run in, and then runs claude inside that environment. Three flavors of isolation Isolarium offers three flavors of isolation that make different trade-offs between security and overhead: Nono - the most lightweight yet least secure option since the agent has access to some of the host’s filesystem. Container - more overhead due to image and container creation yet more secure since only the working tree is shared with the host. Virtual machine - slow to provision but provides the strongest isolation since the agent has no access to the host’s filesystem. What’s more the coding agent has more freedom: e.g., run tests that use Testcontainers. Isolarium works with i2code implement The i2code implement command described in the previous article implements the final step of the Idea to Code workflow , which turns a plan derived from an idea into a pull request consisting of production code and tests. It can now use Isolarium to run the coding agent in a secure, isolated environment: $ isolarium implement –isolation-type < type > … This command runs the i2code implement command inside an Isolarium environment with the specified isolation type. Next steps To learn more about Isolarium and to get started, check out the GitHub repository . I welcome your questions, feedback, and contributions. Need help with modernizing your architecture? I help organizations modernize safely and avoid creating a modern legacy system — a new architecture with the same old problems. If you’re planning or struggling with a modernization effort, I can help. Learn more about my modernization and architecture advisory work →