modify_file · Mcp Ux Vision MCP: Risk & Policy

WHAT IT DOES

What modify_file does on Mcp Ux Vision

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

WHY IT NEEDS A POLICY

Why modify_file needs a policy

The tool creates or modifies data reversibly by editing file contents. While not destructive (data isn't deleted), it has high severity because an AI agent could maliciously modify sensitive files, configuration files, source code, or other critical system files. The ability to target specific line ranges makes surgical modifications possible.

From the tool's definition Tool is named 'modify_file' and explicitly described as 'Modify content in a file between specified line numbers' - this directly performs file modification, a reversible write operation that can alter configuration files, code, or other important data.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

modify_file Rate-limited

modify_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": {
    "modify_file": {
      "limits": [
        {
          "counter": "modify_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 Ux Vision, so you can run agents against it safely.

FAQ

Questions about modify_file

What does the modify_file tool do? +

Modify content in a file between specified line numbers. It is categorised as a Write tool in the Mcp Ux Vision MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on modify_file? +

Register the Mcp Ux Vision MCP server in PolicyLayer and add a rule for modify_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 Ux Vision. Nothing to install.

What risk level is modify_file? +

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

Can I rate-limit modify_file? +

Yes. Add a rate_limit block to the modify_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 modify_file completely? +

Set action: deny in the PolicyLayer policy for modify_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 modify_file? +

modify_file is provided by the Mcp Ux Vision MCP server (sfearl1/mcp-ux-vision). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.