step_into · MCP JS Debugger MCP: Risk & Policy

WHAT IT DOES

What step_into does on MCP JS Debugger

AI agents invoke step_into to trigger actions in MCP JS Debugger. 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 step_into needs a policy

This tool controls debugger execution flow by stepping into function calls or advancing to the next statement. It triggers external operations within the debugging session — advancing code execution — which classifies it as Execute. Misuse could cause unintended code execution paths in a live debugging session, warranting medium severity.

From the tool's definition Steps into a function call if the current line contains one, otherwise steps to the next statement.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

step_into Rate-limited

step_into 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": {
    "step_into": {
      "limits": [
        {
          "counter": "step_into_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 MCP JS Debugger, so you can run agents against it safely.

FAQ

Questions about step_into

What does the step_into tool do? +

Steps into a function call if the current line contains one, otherwise steps to the next statement. It is categorised as a Execute tool in the MCP JS Debugger MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on step_into? +

Register the MCP JS Debugger MCP server in PolicyLayer and add a rule for step_into: 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 MCP JS Debugger. Nothing to install.

What risk level is step_into? +

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

Can I rate-limit step_into? +

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

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

step_into is provided by the MCP JS Debugger MCP server (johngrimes/mcp-js-debugger). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.