evaluate_on_call_frame

THE RISK

High Risk

Why evaluate_on_call_frame needs a policy

This tool executes arbitrary JavaScript code within a paused call frame's context. Running arbitrary JS in a browser context can access/modify DOM, exfiltrate data, manipulate application state, or trigger further actions — making it an Execute-class tool with high severity due to the unrestricted nature of JavaScript execution in a live debugging session.

From the tool's definition Evaluate a JavaScript expression in the context of a specific call frame when paused

Documented attack patterns abuse exactly the kind of access evaluate_on_call_frame gives an agent:

POLICY

How to control evaluate_on_call_frame

PolicyLayer is an MCP gateway — it sits between your AI agents and ReverseCraft DevTools MCP, and nothing reaches the server without passing your rules. This is the rule we recommend for evaluate_on_call_frame:

policy.json

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

evaluate_on_call_frame 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.

Create a free account and register ReverseCraft DevTools MCP — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

RATE-LIMIT THIS TOOL →

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EXPLORE

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All 46 ReverseCraft DevTools MCP tools →

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Go deeper

High-risk tools in ReverseCraft DevTools MCP → Every high-risk tool this server exposes, in one view.
All high-risk MCP tools → Every high-risk tool across the catalogue, and the policy pattern that contains them.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Agent sandbox → Bounding what an agent can execute and where the boundary should sit.
Least privilege for MCP → Granting agents the minimum tool surface the task needs.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about evaluate_on_call_frame

What does the evaluate_on_call_frame tool do? +

Evaluate a JavaScript expression in the context of a specific call frame when paused. It is categorised as a Execute tool in the ReverseCraft DevTools MCP MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on evaluate_on_call_frame? +

Register the ReverseCraft DevTools MCP server in PolicyLayer and add a rule for evaluate_on_call_frame: 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 ReverseCraft DevTools MCP. Nothing to install.

What risk level is evaluate_on_call_frame? +

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

Can I rate-limit evaluate_on_call_frame? +

Yes. Add a rate_limit block to the evaluate_on_call_frame 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 evaluate_on_call_frame completely? +

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

evaluate_on_call_frame is provided by the ReverseCraft DevTools MCP server (reverse-craft/rc-devtools-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every ReverseCraft DevTools MCP tool call.

Start from ReverseCraft DevTools MCP, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →