performance_get_metrics

THE RISK

Low Risk

Why performance_get_metrics needs a policy

This tool reads and retrieves performance metrics from a browser page (Largest Contentful Paint, First Contentful Paint, Cumulative Layout Shift). It is a read-only analysis operation with no side effects, data modification, or destructive capabilities. Misuse potential is minimal — it can only observe and report metrics.

From the tool's definition Analyzes page performance (Core Web Vitals: LCP, FCP, CLS)

Documented attack patterns abuse exactly the kind of access performance_get_metrics gives an agent:

POLICY

How to control performance_get_metrics

PolicyLayer is an MCP gateway — it sits between your AI agents and Browser-Debugger, and nothing reaches the server without passing your rules. This is the rule we recommend for performance_get_metrics:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "performance_get_metrics": {}
  }
}

performance_get_metrics is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.

Create a free account and register Browser-Debugger — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

CAP THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

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All 14 Browser-Debugger tools →

Read tools on other servers

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Data exfiltration → How read access becomes an exfiltration channel when chained with untrusted content.
MCP token cost → What connecting this server costs in context-window tokens on every request.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about performance_get_metrics

What does the performance_get_metrics tool do? +

Analyzes page performance (Core Web Vitals: LCP, FCP, CLS). It is categorised as a Read tool in the Browser-Debugger MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on performance_get_metrics? +

Register the Browser-Debugger MCP server in PolicyLayer and add a rule for performance_get_metrics: 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 Browser-Debugger. Nothing to install.

What risk level is performance_get_metrics? +

performance_get_metrics is a Read tool with low risk. Read-only tools are generally safe to allow by default.

Can I rate-limit performance_get_metrics? +

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

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

performance_get_metrics is provided by the Browser-Debugger MCP server (selvadinesh-giga/mcp-based-browser-debug-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Browser-Debugger tool call.

Start from Browser-Debugger, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →