nexti · Rr MCP: Risk & Policy

WHAT IT DOES

What nexti does on Rr

AI agents invoke nexti to trigger actions in Rr. 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 nexti needs a policy

The tool actively executes/advances the target process by one machine instruction in an rr debugging session. It triggers execution of code in the debugged process, which constitutes an Execute action. While it's a controlled single-step in a debugger, it causes the target program to run code and can have side effects depending on what instruction is executed.

From the tool's definition 'Step forward one machine instruction, stepping over call instructions' — this advances execution state in a live debugging session

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

nexti Rate-limited

nexti 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": {
    "nexti": {
      "limits": [
        {
          "counter": "nexti_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 Rr, so you can run agents against it safely.

FAQ

Questions about nexti

What does the nexti tool do? +

Step forward one machine instruction, stepping over call instructions. It is categorised as a Execute tool in the Rr MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on nexti? +

Register the Rr MCP server in PolicyLayer and add a rule for nexti: 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 Rr. Nothing to install.

What risk level is nexti? +

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

Can I rate-limit nexti? +

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

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

nexti is provided by the Rr MCP server (jnjaeschke/rr-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.