files_write_lines · Promethean OS MCP: Risk & Policy

WHAT IT DOES

What files_write_lines does on Promethean OS MCP

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

WHY IT NEEDS A POLICY

Why files_write_lines needs a policy

This tool creates or modifies file data reversibly by appending or inserting lines. It does not delete or irreversibly overwrite files (which would be Destructive), nor does it execute code or trigger external operations (which would be Execute).

From the tool's definition Tool name 'files_write_lines' and description 'Append or insert lines into a file' indicate modification of file content. The operation is reversible (lines can be edited or removed), distinguishing it from destructive operations.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

files_write_lines Rate-limited

files_write_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": {
    "files_write_lines": {
      "limits": [
        {
          "counter": "files_write_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 Promethean OS MCP, so you can run agents against it safely.

FAQ

Questions about files_write_lines

What does the files_write_lines tool do? +

Append or insert lines into a file at startLine (1-based). It is categorised as a Write tool in the Promethean OS MCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on files_write_lines? +

Register the Promethean OS MCP server in PolicyLayer and add a rule for files_write_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 Promethean OS MCP. Nothing to install.

What risk level is files_write_lines? +

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

Can I rate-limit files_write_lines? +

Yes. Add a rate_limit block to the files_write_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 files_write_lines completely? +

Set action: deny in the PolicyLayer policy for files_write_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 files_write_lines? +

files_write_lines is provided by the Promethean OS MCP server (octave-commons/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.