set_default_backend · Omni Fs MCP: Risk & Policy

WHAT IT DOES

What set_default_backend does on Omni Fs

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

WHY IT NEEDS A POLICY

Why set_default_backend needs a policy

This tool creates or modifies configuration data reversibly (the default can be changed again), making it a Write operation rather than Read or Execute. It does not delete data (not Destructive), move money (not Financial), or directly execute arbitrary commands (not Execute).

From the tool's definition The tool modifies configuration state by setting a default backend preference. The description states 'Set the default backend for operations when no backend is specified,' which indicates it changes system configuration that affects subsequent operations.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

set_default_backend Rate-limited

set_default_backend 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": {
    "set_default_backend": {
      "limits": [
        {
          "counter": "set_default_backend_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 Omni Fs, so you can run agents against it safely.

FAQ

Questions about set_default_backend

What does the set_default_backend tool do? +

Set the default backend for operations when no backend is specified. It is categorised as a Write tool in the Omni Fs MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on set_default_backend? +

Register the Omni Fs MCP server in PolicyLayer and add a rule for set_default_backend: 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 Omni Fs. Nothing to install.

What risk level is set_default_backend? +

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

Can I rate-limit set_default_backend? +

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

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

set_default_backend is provided by the Omni Fs MCP server (vaayne/omni-fs-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.