start_screencast · Chromium ARM64 Browser MCP: Risk & Policy

WHAT IT DOES

What start_screencast does on Chromium ARM64 Browser

AI agents invoke start_screencast to trigger actions in Chromium ARM64 Browser. 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.

WHY IT NEEDS A POLICY

Why start_screencast needs a policy

This is an Execute category tool because it initiates and controls an external operation (screencast recording via CDP) with effects that vary based on parameters and duration. While it does not permanently delete data (not Destructive) or modify persistent application state (not Write), it actively executes browser instrumentation and media encoding processes.

From the tool's definition Tool 'start_screencast' records browser activity through CDP (Chrome DevTools Protocol) and encodes video output.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

start_screencast Rate-limited

start_screencast 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": {
    "start_screencast": {
      "limits": [
        {
          "counter": "start_screencast_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 Chromium ARM64 Browser, so you can run agents against it safely.

FAQ

Questions about start_screencast

What does the start_screencast tool do? +

Start recording a screencast of browser activity. Captures frames via CDP and encodes to MP4/GIF/WebM on stop. It is categorised as a Execute tool in the Chromium ARM64 Browser MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on start_screencast? +

Register the Chromium ARM64 Browser MCP server in PolicyLayer and add a rule for start_screencast: 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 Chromium ARM64 Browser. Nothing to install.

What risk level is start_screencast? +

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

Can I rate-limit start_screencast? +

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

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

start_screencast is provided by the Chromium ARM64 Browser MCP server (nfodor/mcp-chromium-arm64). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.