browser_cdp_performance_metrics
Atomic primitive: fetch browser runtime metrics via CDP Performance.getMetrics() on the active page. Returns raw CDP-level counters (LayoutCount, RecalcStyleCount, ScriptDuration, TaskDuration, JSHeapUsedSize, Nodes, Documents, Frames, ...) — not Web Vitals (use browser_get_metrics for those).
This record as markdown: /tools/io-github-vmoranv-jshookmcp/browser-cdp-performance-metrics.md
What browser_cdp_performance_metrics does on Jshookmcp
AI agents call browser_cdp_performance_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.
Why browser_cdp_performance_metrics is rated Low
Retrieves read-only performance counters from the browser; no side effects.
From the tool's definition fetch browser runtime metrics via CDP Performance.getMetrics()
Attacks that exploit this kind of access
The rule that runs browser_cdp_performance_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_cdp_performance_metrics, this is the rule to start with:
browser_cdp_performance_metrics is read-only, so it stays allowed. Everything else on the server is denied unless you say otherwise.
The button opens the PolicyLayer dashboard: create your workspace, connect Jshookmcp, apply this rule, and every browser_cdp_performance_metrics call is checked against it from then on.
Questions about browser_cdp_performance_metrics
Atomic primitive: fetch browser runtime metrics via CDP Performance.getMetrics() on the active page. Returns raw CDP-level counters (LayoutCount, RecalcStyleCount, ScriptDuration, TaskDuration, JSHeapUsedSize, Nodes, Documents, Frames, ...) — not Web Vitals (use browser_get_metrics for those). It is categorised as a Read tool in the Jshookmcp MCP Server, which means it retrieves data without modifying state.
Register the Jshook MCP server in PolicyLayer and add a rule for browser_cdp_performance_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.
browser_cdp_performance_metrics is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the browser_cdp_performance_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.
Set action: deny in the PolicyLayer policy for browser_cdp_performance_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.
browser_cdp_performance_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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