file_write · Lockstep MCP: Risk & Policy

WHAT IT DOES

What file_write does on Lockstep

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

WHY IT NEEDS A POLICY

Why file_write needs a policy

The tool creates or modifies file content, which is characteristic of the Write category. Severity is medium because unintended file modifications could corrupt project files, but the effect is reversible (files can be restored/rewritten).

From the tool's definition Tool name 'file_write' with description 'Write a file' indicates creation or modification of files. This is a reversible write operation.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

file_write Rate-limited

file_write 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": {
    "file_write": {
      "limits": [
        {
          "counter": "file_write_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 Lockstep, so you can run agents against it safely.

FAQ

Questions about file_write

What does the file_write tool do? +

Write a file. It is categorised as a Write tool in the Lockstep MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on file_write? +

Register the Lockstep MCP server in PolicyLayer and add a rule for file_write: 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 Lockstep. Nothing to install.

What risk level is file_write? +

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

Can I rate-limit file_write? +

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

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

file_write is provided by the Lockstep MCP server (tmmoore286/lockstep-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.