connect · Nrepl MCP: Risk & Policy

WHAT IT DOES

What connect does on Nrepl

AI agents invoke connect to trigger actions in Nrepl. 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.

PARAMETERS

Parameter	Type	Required	Description
`host`	string	Yes	nREPL server host
`port`	number	Yes	nREPL server port

Parameters from the server's own tool schema.

WHY IT NEEDS A POLICY

Why connect needs a policy

This tool establishes a network connection to an nREPL (networked REPL) server, which is an external operation with side effects. Once connected, an AI agent gains the ability to evaluate arbitrary Clojure code on the remote server (as evidenced by sibling tool 'eval_form'). Initiating this connection is a prerequisite for arbitrary code execution, making it high severity.

From the tool's definition Connect to an nREPL server. Example: (connect {:host "localhost" :port 1234})

Risk signalsAccepts URL/endpoint input (host)

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

connect Rate-limited

connect 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": {
    "connect": {
      "limits": [
        {
          "counter": "connect_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 Nrepl, so you can run agents against it safely.

FAQ

Questions about connect

What does the connect tool do? +

Connect to an nREPL server. Example: (connect {:host "localhost" :port 1234}). It is categorised as a Execute tool in the Nrepl MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

What parameters does connect accept? +

connect accepts 2 parameters: host, port. Required: host, port. The full parameter table on this page comes from the server's own tool schema.

How do I enforce a policy on connect? +

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

What risk level is connect? +

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

Can I rate-limit connect? +

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

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

connect is provided by the Nrepl MCP server (nrepl-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.