vibe_preview_start · Yaver MCP: Risk & Policy

WHAT IT DOES

What vibe_preview_start does on Yaver

AI agents invoke vibe_preview_start to trigger actions in Yaver. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

PARAMETERS

Parameter	Type	Required	Description
`mode`	string	—	Capture cadence; default live
`profile`	string	—	Optional profile override: live-direct \| live-relay-wifi \| live-relay-cell \| change-only \| summary-only
`project`	string	Yes	Project name (used as session key)
`target_url`	string	Yes	Dev server URL to capture (e.g. http://127.0.0.1:3000)

Parameters from the server's own tool schema.

WHY IT NEEDS A POLICY

Why vibe_preview_start needs a policy

vibe_preview_start triggers real processes with real consequences. An agent gone sideways doesn't fire it once — it starts dozens of builds, sends mass notifications, or burns through compute before anyone looks up.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

vibe_preview_start Rate-limited

vibe_preview_start stays usable, but rate-capped — a runaway agent can't fire it dozens of times 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_start": {
      "limits": [
        {
          "counter": "vibe_preview_start_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Yaver, so you can run agents against it safely.

FAQ

Questions about vibe_preview_start

What does the vibe_preview_start tool do? +

Start a vibe-preview session: headless Chrome captures the dev server URL at adaptive FPS. The mobile app + web dashboard see the same SSE stream you do. Returns the session metadata. It is categorised as a Execute tool in the Yaver MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

What parameters does vibe_preview_start accept? +

vibe_preview_start accepts 4 parameters: mode, profile, project, target_url. Required: project, target_url. The full parameter table on this page comes from the server's own tool schema.

How do I enforce a policy on vibe_preview_start? +

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

What risk level is vibe_preview_start? +

vibe_preview_start is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit vibe_preview_start? +

Yes. Add a rate_limit block to the vibe_preview_start 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_start completely? +

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

vibe_preview_start is provided by the Yaver MCP server (yaver-cli). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.