vibe_preview · VibeServe MCP: Risk & Policy

WHAT IT DOES

What vibe_preview does on VibeServe

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

WHY IT NEEDS A POLICY

Why vibe_preview needs a policy

The tool creates new files (an HTML preview page and a Playwright test script), which is a Write operation. It does not execute code, delete data, or move money. The blast radius is medium because it produces files on disk that could contain arbitrary content, but the action is reversible.

From the tool's definition Generate a preview HTML page and Playwright test script

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

vibe_preview Rate-limited

vibe_preview 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": {
    "vibe_preview": {
      "limits": [
        {
          "counter": "vibe_preview_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 VibeServe, so you can run agents against it safely.

FAQ

Questions about vibe_preview

What does the vibe_preview tool do? +

Generate a preview HTML page and Playwright test script. It is categorised as a Write tool in the VibeServe MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on vibe_preview? +

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

What risk level is vibe_preview? +

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

Can I rate-limit vibe_preview? +

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

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

vibe_preview is provided by the VibeServe MCP server (ncsound919/vibeserve). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.