Evaluates a JavaScript expression in the context of a specific call frame while paused. This allows you to inspect variables and execute code in the paused scope.
AI agents invoke evaluate_on_callframe to trigger actions in JS Reverse Strong MCP. 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.
This tool executes arbitrary JavaScript expressions within a debugger context. While scoped to a paused call frame (which limits blast radius compared to unrestricted code execution), it still permits running code with side effects determined by the user's input. The effect depends on what expression is passed as an argument, making this an Execute-category tool rather than a passive Read operation.
From the tool's definition Tool name 'evaluate_on_callframe' and description stating it 'Evaluates a JavaScript expression in the context of a specific call frame while paused' and 'execute code in the paused scope' indicates arbitrary code execution capability.
Documented attack patterns abuse exactly the kind of access evaluate_on_callframe gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and JS Reverse Strong MCP, and nothing reaches the server without passing your rules. This is the rule we recommend for evaluate_on_callframe:
{
"version": "1",
"default": "deny",
"tools": {
"evaluate_on_callframe": {
"limits": [
{
"counter": "evaluate_on_callframe_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}evaluate_on_callframe 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.
Free to start. No card required.
Evaluates a JavaScript expression in the context of a specific call frame while paused. This allows you to inspect variables and execute code in the paused scope. It is categorised as a Execute tool in the JS Reverse Strong MCP MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the JS Reverse Strong MCP server in PolicyLayer and add a rule for evaluate_on_callframe: 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 JS Reverse Strong MCP. Nothing to install.
evaluate_on_callframe 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_on_callframe 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_on_callframe. 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_on_callframe is provided by the JS Reverse Strong MCP server (lwjjike/jsreverser-strong-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from JS Reverse Strong MCP, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
85 JS Reverse Strong MCP tools catalogued and risk-classified — across an index of 43,000+ MCP servers.