create_file · Filesystem MCP Server MCP: Risk & Policy

WHAT IT DOES

What create_file does on Filesystem MCP Server

AI agents use create_file to create or update resources in Filesystem MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Filesystem MCP Server environment.

WHY IT NEEDS A POLICY

Why create_file needs a policy

The create_file tool creates new files, which is a reversible write operation that modifies the filesystem state but does not irreversibly destroy data or execute arbitrary code. The sandboxing mitigation limits blast radius to the allowed directory set, lowering severity from high to medium.

From the tool's definition Tool name 'create_file' and sibling tools including 'edit_file', 'delete_file', 'move_file' indicate write/modify capabilities.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

create_file Rate-limited

create_file 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.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "create_file": {
      "limits": [
        {
          "counter": "create_file_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

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PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Filesystem MCP Server, so you can run agents against it safely.

FAQ

Questions about create_file

What does the create_file tool do? +

create_file. It is categorised as a Write tool in the Filesystem MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on create_file? +

Register the Filesystem MCP Server MCP server in PolicyLayer and add a rule for create_file: 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 Filesystem MCP Server. Nothing to install.

What risk level is create_file? +

create_file is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit create_file? +

Yes. Add a rate_limit block to the create_file 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.

How do I block create_file completely? +

Set action: deny in the PolicyLayer policy for create_file. 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.

What MCP server provides create_file? +

create_file is provided by the Filesystem MCP Server MCP server (preston-harrison/fs-mcp-py). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.