write_file

Create a new file or completely overwrite an existing file

SERVERNcp SOURCE@portel/ncp

Medium RISK CLASS

Category Write

Parameters 00 required

Recommended Rate-limitedsee the rule below

Registry record Grade F, identity unverified Pull the record →

This record as markdown: /tools/io-github-portel-dev-ncp/write-file.md

WHAT IT DOES

What write_file does on Ncp

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

RISK

Why write_file is rated Medium

This tool creates or modifies files, which is a reversible Write operation. However, it can overwrite existing files completely, giving it high severity due to potential data loss and side effects on the system. It does not delete files (which would be Destructive) but the overwrite capability on existing files elevates the risk beyond a simple create operation.

From the tool's definition Tool name 'write_file' and description states 'Create a new file or completely overwrite an existing file'

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs write_file safely

PolicyLayer is an MCP gateway: it sits between your AI agents and Ncp, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For write_file, this is the rule to start with:

write_file Rate-limited

write_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_file": {
      "limits": [
        {
          "counter": "write_file_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL → Instant setup, no code required.

The button opens the PolicyLayer dashboard: create your workspace, connect Ncp, apply this rule, and every write_file call is checked against it from then on.

FAQ

Questions about write_file

What does the write_file tool do? +

Create a new file or completely overwrite an existing file. It is categorised as a Write tool in the Ncp 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_file? +

Register the Ncp MCP server in PolicyLayer and add a rule for write_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 Ncp. Nothing to install.

What risk level is write_file? +

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

Can I rate-limit write_file? +

Yes. Add a rate_limit block to the write_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_file completely? +

Set action: deny in the PolicyLayer policy for write_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_file? +

write_file is provided by the Ncp MCP server (@portel/ncp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

KEEP EXPLORING

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