browser_get_metrics

SERVERJshookmcp SOURCE@jshookmcp/jshook

Low RISK CLASS

Category Read

Parameters 00 required

Recommended Allowedsee the rule below

Registry record Grade F, identity unverified Pull the record →

This record as markdown: /tools/io-github-vmoranv-jshookmcp/browser-get-metrics.md

WHAT IT DOES

What browser_get_metrics does on Jshookmcp

AI agents call browser_get_metrics to retrieve information from Jshookmcp without modifying anything. It is typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.

RISK

Why browser_get_metrics is rated Low

Tool passively gathers performance telemetry without modifying state or executing arbitrary code.

From the tool's definition collect page performance metrics, Web Vitals, DOM timing, JS heap sizes

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs browser_get_metrics safely

PolicyLayer is an MCP gateway: it sits between your AI agents and Jshookmcp, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For browser_get_metrics, this is the rule to start with:

browser_get_metrics Allowed

browser_get_metrics is read-only, so it stays allowed. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

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

ALLOW ONLY THIS TOOL → Instant setup, no code required.

The button opens the PolicyLayer dashboard: create your workspace, connect Jshookmcp, apply this rule, and every browser_get_metrics call is checked against it from then on.

FAQ

Questions about browser_get_metrics

What does the browser_get_metrics tool do? +

Atomic primitive: collect page performance metrics via PerformanceMonitor — Web Vitals (FCP, LCP, CLS, TTFB), DOM timing (domContentLoaded, loadComplete), engine-level counters (scriptDuration, layoutDuration, recalcStyleDuration) and JS heap sizes (usedJSHeapSize / totalJSHeapSize / jsHeapSizeLimit). Optionally include the raw performance timeline entries. Replaces the legacy network-domain performance_get_metrics (still working as a backward-compat alias). It is categorised as a Read tool in the Jshookmcp MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on browser_get_metrics? +

Register the Jshook MCP server in PolicyLayer and add a rule for browser_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 Jshookmcp. Nothing to install.

What risk level is browser_get_metrics? +

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

Can I rate-limit browser_get_metrics? +

Yes. Add a rate_limit block to the browser_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 browser_get_metrics completely? +

Set action: deny in the PolicyLayer policy for browser_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 browser_get_metrics? +

browser_get_metrics is provided by the Jshook MCP server (@jshookmcp/jshook). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

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