mcp_write_file_safe · Local Code MCP: Risk & Policy

WHAT IT DOES

What mcp_write_file_safe does on Local Code

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

WHY IT NEEDS A POLICY

Why mcp_write_file_safe needs a policy

This tool creates or modifies text files (Write category). It is reversible because backups are created before overwriting existing files, preventing it from being Destructive. The backup mechanism and emphasis on 'safe' in the name mitigate risk compared to an unguarded write operation. Severity is medium because an AI agent could still corrupt important source code files, though recovery is possible via the backup.

From the tool's definition Tool name is 'mcp_write_file_safe' with description stating it 'Write[s] a text file' and creates a backup for existing files. The word 'Write' directly indicates file creation/modification, and the backup mechanism suggests reversibility.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

mcp_write_file_safe Rate-limited

mcp_write_file_safe 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": {
    "mcp_write_file_safe": {
      "limits": [
        {
          "counter": "mcp_write_file_safe_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

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Instant setup, no code required.

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

FAQ

Questions about mcp_write_file_safe

What does the mcp_write_file_safe tool do? +

Write a text file after creating a backup when the file already exists. It is categorised as a Write tool in the Local Code MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on mcp_write_file_safe? +

Register the Local Code MCP server in PolicyLayer and add a rule for mcp_write_file_safe: 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 Local Code. Nothing to install.

What risk level is mcp_write_file_safe? +

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

Can I rate-limit mcp_write_file_safe? +

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

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

mcp_write_file_safe is provided by the Local Code MCP server (js190-prog/local-code-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.