Claude Code Mods Aren't Sandboxed. Neither Is Your Understanding of "Sandboxed".
Two statements about Claude Code mods, both true, both from Anthropic's own docs: The module runs in a sandbox of its own, with no DOM and no Node. "Mods aren't sandboxed." The first two days of the mods launch have been one long argument about which of these is the lie. Neither is.
The article explores the concept of sandboxing in Claude Code mods, highlighting the confusion around the term 'sandboxed' and the actual security boundaries in place.
What happened
The article discusses the confusion around the term 'sandboxed' in the context of Claude Code mods. It explains that while the JavaScript runtime is sandboxed, the mods themselves are not sandboxed in terms of system access. The article highlights the security implications of this and the importance of understanding the actual trust boundaries.
Why it matters
For AI developers and security professionals, understanding the true nature of sandboxing in Claude Code is crucial for assessing the risks associated with using mods. This knowledge helps in making informed decisions about trust and security when integrating such tools into workflows.
- Sandboxing in Claude Code refers to two different aspects: the JavaScript runtime and system access.
- Mods can access user files, processes, and network resources, which requires careful validation.
- The permission prompt is a critical security boundary that cannot be modified by mods.
- Users should validate mods before installation and understand their capabilities to ensure security.
- The article emphasizes the need for a clear mental model of mod behavior to avoid security pitfalls.
The bigger picture
The article's insights have a significant impact on how users and developers approach the use of Claude Code mods. It underscores the importance of validating mods before installation and understanding their capabilities to mitigate potential security risks.
The article clarifies the confusion around sandboxing in Claude Code mods, emphasizing the importance of understanding the actual security boundaries and the need for careful validation before installation.
Technical details
- JavaScript runtime sandboxing restricts access to the DOM and Node.js globals.
- Mods use the $ API to interact with external resources, which allows the engine to log and gate these interactions.
- Mods can access user files, start processes, and make network requests, which are not restricted by the JavaScript sandbox.
- The permission prompt is a critical UI element that cannot be modified by mods, ensuring user control over security decisions.
FAQ
What does it mean for Claude Code mods to be sandboxed?
Claude Code mods are sandboxed in terms of the JavaScript runtime, which restricts access to the DOM and Node.js globals. However, they are not sandboxed in terms of system access, as they can read files, start processes, and make network requests.
Why is the permission prompt important in Claude Code?
The permission prompt is a critical security boundary that cannot be modified by mods. It ensures that users have control over security decisions, preventing mods from faking or altering the prompt.
What should users do before installing a Claude Code mod?
Users should validate mods before installation by reviewing the validation checklist, understanding the capabilities of the mod, and ensuring they trust the source.
Can a mod rewrite events in Claude Code?
Yes, a mod can observe, rewrite, or fully answer any event, including those that an audit logger was counting on. This highlights the potential security risks associated with mods.
What is the recommended approach for managing Claude Code mods?
Users should install mods only from trusted sources, understand their capabilities, and use features like safe mode or disableAllHooks to manage security settings effectively.
This summary and analysis were generated with AI from the original article and may contain errors. Read the original for the full story.
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Originally published by Dev.to AI on Oct 4, 2026.
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