performance_start_trace · Chrome Devtools MCP: Risk & Policy

WHAT IT DOES

What performance_start_trace does on Chrome Devtools

AI agents invoke performance_start_trace to trigger actions in Chrome Devtools. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

WHY IT NEEDS A POLICY

Why performance_start_trace needs a policy

Performance tracing starts an active monitoring operation on the webpage, which is an executable action that instruments the browser runtime. While it does not directly modify page data or execute arbitrary user code (which would make it higher severity), it triggers browser-level operations whose effects depend on the target webpage's state and configuration.

From the tool's definition Tool description states 'Start a performance trace on the selected webpage' and tool name contains 'start_trace', indicating it initiates a tracing operation that instruments and monitors a live browser process.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

performance_start_trace Rate-limited

performance_start_trace stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "performance_start_trace": {
      "limits": [
        {
          "counter": "performance_start_trace_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Chrome Devtools, so you can run agents against it safely.

FAQ

Questions about performance_start_trace

What does the performance_start_trace tool do? +

Start a performance trace on the selected webpage. Use to find frontend performance issues, Core Web Vitals (LCP, INP, CLS), and improve page load speed. It is categorised as a Execute tool in the Chrome Devtools MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on performance_start_trace? +

Register the Chrome Devtools MCP server in PolicyLayer and add a rule for performance_start_trace: 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 Chrome Devtools. Nothing to install.

What risk level is performance_start_trace? +

performance_start_trace is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit performance_start_trace? +

Yes. Add a rate_limit block to the performance_start_trace 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_start_trace completely? +

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

performance_start_trace is provided by the Chrome Devtools MCP server (shivamprasad99/chrome-devtools-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.