AI agents call performance_metrics to retrieve information from OpenChrome without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool reads and returns performance metrics from the browser page. It does not modify, execute, or delete anything. The blast radius if misused is minimal — at worst it leaks timing/performance data about a page.
From the tool's definition "Get page performance metrics" — retrieves performance data from the current page with no side effects
Documented attack patterns abuse exactly the kind of access performance_metrics gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and OpenChrome, and nothing reaches the server without passing your rules. This is the rule we recommend for performance_metrics:
{
"version": "1",
"default": "deny",
"tools": {
"performance_metrics": {}
}
}performance_metrics is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Get page performance metrics. It is categorised as a Read tool in the OpenChrome MCP Server, which means it retrieves data without modifying state.
Register the OpenChrome MCP server in PolicyLayer and add a rule for 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 OpenChrome. Nothing to install.
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 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 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.
performance_metrics is provided by the OpenChrome MCP server (shaun0927/openchrome). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 106 OpenChrome tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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106 OpenChrome tools catalogued and risk-classified — across an index of 42,500+ MCP servers.