insert_lines · MCP Start App MCP: Risk & Policy

WHAT IT DOES

What insert_lines does on MCP Start App

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

WHY IT NEEDS A POLICY

Why insert_lines needs a policy

This tool creates or modifies file content in a reversible manner. While it changes files, insertions are not destructive—the operation can be undone by deleting the inserted lines. It does not execute code, delete data irreversibly, or move money.

From the tool's definition Tool name 'insert_lines' and description 'Insert new lines at a specific position in the file' indicate file modification capability. The sibling tool 'delete_lines' and 'edit_file_lines' confirm this server handles file mutations.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

insert_lines Rate-limited

insert_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": {
    "insert_lines": {
      "limits": [
        {
          "counter": "insert_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 MCP Start App, so you can run agents against it safely.

FAQ

Questions about insert_lines

What does the insert_lines tool do? +

Insert new lines at a specific position in the file. It is categorised as a Write tool in the MCP Start App MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on insert_lines? +

Register the MCP Start App MCP server in PolicyLayer and add a rule for insert_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 MCP Start App. Nothing to install.

What risk level is insert_lines? +

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

Can I rate-limit insert_lines? +

Yes. Add a rate_limit block to the insert_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 insert_lines completely? +

Set action: deny in the PolicyLayer policy for insert_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 insert_lines? +

insert_lines is provided by the MCP Start App MCP server (nexus-aissam/mcp-local). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.