Create a directory with parent directories inside the sandbox.
AI agents use sandbox_fs_mkdir to create or update resources in Microsandbox — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Microsandbox environment.
The tool creates directories within a sandbox filesystem. This is a Write operation (reversible modification) rather than Destructive since directories can be removed. Severity is medium because creating directories could fill disk space or clutter the filesystem, but the operation is scoped to a sandbox and reversible via sandbox_fs_remove. Confidence is high due to explicit 'Create' language in the description.
From the tool's definition Tool name 'sandbox_fs_mkdir' and description 'Create a directory with parent directories inside the sandbox' indicate directory creation, a reversible modification operation.
Documented attack patterns abuse exactly the kind of access sandbox_fs_mkdir gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Microsandbox, and nothing reaches the server without passing your rules. This is the rule we recommend for sandbox_fs_mkdir:
{
"version": "1",
"default": "deny",
"tools": {
"sandbox_fs_mkdir": {
"limits": [
{
"counter": "sandbox_fs_mkdir_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}sandbox_fs_mkdir stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
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Create a directory with parent directories inside the sandbox. It is categorised as a Write tool in the Microsandbox MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Microsandbox MCP server in PolicyLayer and add a rule for sandbox_fs_mkdir: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Microsandbox. Nothing to install.
sandbox_fs_mkdir is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the sandbox_fs_mkdir rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for sandbox_fs_mkdir. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
sandbox_fs_mkdir is provided by the Microsandbox MCP server (superradcompany/microsandbox-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Microsandbox, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
19 Microsandbox tools catalogued and risk-classified — across an index of 43,000+ MCP servers.