move_lines · Filesystem MCP: Risk & Policy

WHAT IT DOES

What move_lines does on FilesystemMCP

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

WHY IT NEEDS A POLICY

Why move_lines needs a policy

This is a Write operation because it modifies file content in a reversible manner. While the operation involves deletion of lines from their original position, the lines are not permanently lost—they are relocated within the same or allowed files.

From the tool's definition The tool performs 'cut and paste' operations on files—moving (removing from one location and inserting at another) a range of lines within a file.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

move_lines Rate-limited

move_lines 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": {
    "move_lines": {
      "limits": [
        {
          "counter": "move_lines_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 FilesystemMCP, so you can run agents against it safely.

FAQ

Questions about move_lines

What does the move_lines tool do? +

Move a range of lines to after a given line number (cut and paste). Line numbers are adjusted automatically for the removal. Throws if insertAfterLine falls inside the source range. Only works within allowed directories. It is categorised as a Write tool in the FilesystemMCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on move_lines? +

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

What risk level is move_lines? +

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

Can I rate-limit move_lines? +

Yes. Add a rate_limit block to the move_lines 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 move_lines completely? +

Set action: deny in the PolicyLayer policy for move_lines. 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 move_lines? +

move_lines is provided by the Filesystem MCP server (rijadalisic/filesystemmcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.