write_text_file · Nexus Core MCP: Risk & Policy

WHAT IT DOES

What write_text_file does on Nexus Core

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

WHY IT NEEDS A POLICY

Why write_text_file needs a policy

This tool creates or modifies text files reversibly. Files can be overwritten or recreated, but the operation is not inherently destructive since previous versions could theoretically be recovered or the action reversed through normal file system operations.

From the tool's definition Tool description explicitly states "WRITE: create or replace a text file at path." The verb "replace" indicates modification capability, and "create" indicates content generation without deletion.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

write_text_file Rate-limited

write_text_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": {
    "write_text_file": {
      "limits": [
        {
          "counter": "write_text_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 Nexus Core, so you can run agents against it safely.

FAQ

Questions about write_text_file

What does the write_text_file tool do? +

WRITE: create or replace a text file at path. Parent must already exist inside ALLOWED_ROOTS. It is categorised as a Write tool in the Nexus Core MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on write_text_file? +

Register the Nexus Core MCP server in PolicyLayer and add a rule for write_text_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 Nexus Core. Nothing to install.

What risk level is write_text_file? +

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

Can I rate-limit write_text_file? +

Yes. Add a rate_limit block to the write_text_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 write_text_file completely? +

Set action: deny in the PolicyLayer policy for write_text_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 write_text_file? +

write_text_file is provided by the Nexus Core MCP server (noumenon-ai/nexus-core). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.