Get runtime performance metrics (DOM nodes, event listeners, JS heap) (see browser_docs)
AI agents call browser_perf_get_metrics to retrieve information from Browser MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves diagnostic performance data from the browser runtime. It does not create, modify, delete, or execute any code or commands—it only queries and returns metrics about the current state of the page. This is a pure Read operation with minimal security risk, as it only exposes performance telemetry that an attacker could already observe through browser DevTools.
From the tool's definition Tool name and description indicate retrieval of performance metrics: "Get runtime performance metrics (DOM nodes, event listeners, JS heap)".
Attacks that exploit this kind of access
Get runtime performance metrics (DOM nodes, event listeners, JS heap) (see browser_docs). It is categorised as a Read tool in the Browser MCP Server MCP Server, which means it retrieves data without modifying state.
Register the Browser MCP Server MCP server in PolicyLayer and add a rule for browser_perf_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 MCP Server. Nothing to install.
browser_perf_get_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_perf_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.
Set action: deny in the PolicyLayer policy for browser_perf_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.
browser_perf_get_metrics is provided by the Browser MCP Server MCP server (madebytokens/browser-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
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