[STEP 6b] Evaluate any JavaScript expression in the context of the currently paused call frame. Use this to inspect nested objects, call methods, compute derived values, or verify conditions at runtime. Complements getScopeVariables for values not directly visible in scope (e.g. this.state, JSON....
Risk signalsAccepts freeform code/query input (expression)
Part of the Chrome Debugger MCP server.
Free to start. No card required.
AI agents invoke evaluate to trigger processes or run actions in Chrome Debugger MCP. Execute operations can have side effects beyond the immediate call -- triggering builds, sending notifications, or starting workflows. Rate limits and argument validation are essential to prevent runaway execution.
evaluate can trigger processes with real-world consequences. An uncontrolled agent might start dozens of builds, send mass notifications, or kick off expensive compute jobs. PolicyLayer enforces rate limits and validates arguments to keep execution within safe bounds.
Execute tools trigger processes. Rate-limit and validate arguments to prevent unintended side effects.
{
"version": "1",
"default": "deny",
"tools": {
"evaluate": {
"limits": [
{
"counter": "evaluate_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}See the full Chrome Debugger MCP policy for all 18 tools.
These attack patterns abuse exactly the kind of access evaluate gives an agent. Each links to the full case and the policy that stops it:
Other execute tools across the catalogue. The same approach applies to each: rate-limit and validate the arguments.
[STEP 6b] Evaluate any JavaScript expression in the context of the currently paused call frame. Use this to inspect nested objects, call methods, compute derived values, or verify conditions at runtime. Complements getScopeVariables for values not directly visible in scope (e.g. this.state, JSON.stringify(obj)).. It is categorised as a Execute tool in the Chrome Debugger MCP MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Chrome Debugger MCP server in PolicyLayer and add a rule for evaluate: 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 Debugger MCP. Nothing to install.
evaluate is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the evaluate 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 evaluate. 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.
evaluate is provided by the Chrome Debugger MCP server (chrome-debugger-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 18 Chrome Debugger MCP tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
4,600+ MCP servers and 31,000+ tools scanned and risk-classified.