create_file · MCP Tools MCP: Risk & Policy

WHAT IT DOES

What create_file does on MCP Tools

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

WHY IT NEEDS A POLICY

Why create_file needs a policy

This tool creates new files in the local environment. While it cannot overwrite existing files (fails if file already exists), it can still write content to the filesystem, which constitutes a Write operation. Severity is high rather than medium because unrestricted file creation could fill disk space, overwrite critical system files if path validation is weak, or create malicious scripts.

From the tool's definition Tool description: 'Create a new file with the given content.' The verb 'Create' and the action of writing content to a new file are the primary operations.

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"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

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

FAQ

Questions about create_file

What does the create_file tool do? +

Create a new file with the given content. Fails if file already exists. It is categorised as a Write tool in the MCP Tools 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 MCP Tools 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 MCP Tools. 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 MCP Tools MCP server (joehuangcoding/mcp-tools). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.