fs_replace · E MCP: Risk & Policy

WHAT IT DOES

What fs_replace does on Emcp

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

WHY IT NEEDS A POLICY

Why fs_replace needs a policy

fs_replace most likely creates or modifies file contents reversibly, classifying as Write rather than Destructive (which would require permanent deletion/overwrite without recovery). The lack of a description lowers confidence slightly, but the tool name and server context strongly suggest file modification semantics.

From the tool's definition Tool name 'fs_replace' indicates file replacement/modification. Server description confirms 'filesystem operations' capability. No description provided, but naming convention parallels other filesystem tools (fs_read, fs_write, fs_rm) that modify files.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

fs_replace Rate-limited

fs_replace 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": {
    "fs_replace": {
      "limits": [
        {
          "counter": "fs_replace_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 Emcp, so you can run agents against it safely.

FAQ

Questions about fs_replace

What does the fs_replace tool do? +

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

How do I enforce a policy on fs_replace? +

Register the E MCP server in PolicyLayer and add a rule for fs_replace: 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 Emcp. Nothing to install.

What risk level is fs_replace? +

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

Can I rate-limit fs_replace? +

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

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

fs_replace is provided by the E MCP server (slezica/emcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.