nodejs-repl-mcp

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Create REPL session

create_session

Creates a named, persistent Node.js REPL session with an isolated child process. Variables, declarations, required modules, and top-level await state carry across evaluations until the session is removed.

Instructions

Create a named, persistent Node.js REPL session. Each session runs in its own child process with an isolated context: variables, let/const declarations, required modules and top-level await state persist across exec calls until the session is removed.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "name": "<name>"
    },
    "name": "create_session"
  }
}

Input Schema

Name	Required	Description	Default
`name`	Yes	Session name (alphanumeric, -, _; max 64 chars)

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Sep 2, 2026

TDQS

A4.4/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries the full burden of behavioral disclosure. It clearly explains that each session runs in its own child process, has an isolated context, preserves runtime state across exec calls, and persists until removed. This gives the agent important behavioral expectations without needing annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is two sentences and front-loads the core purpose before adding behavioral detail. There is no redundancy, and every sentence contributes useful information for correct usage.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a one-parameter tool with no output schema, the description is quite complete: it explains persistence, isolation, and lifespan. It does not mention duplicate-name behavior or the exact response shape, but those are minor gaps for a simple creation tool.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The schema fully documents the single `name` parameter with type, pattern, and description. The tool description adds little param-specific detail beyond referring to the session as 'named', so the schema already does the heavy lifting. Baseline 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb and resource: creating a named, persistent Node.js REPL session. It also distinguishes itself from siblings by explaining that session state persists across exec calls and is removed only via removal, making its role clear.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides clear context for when to use the tool: when a persistent, isolated REPL session is needed, as opposed to just executing one-off code. It does not explicitly name alternatives or state when not to use it, but the context around child-process isolation and persistence is strong enough.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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