dynamic-mcp

Run JS Ephemeral

run_js_ephemeral

Execute one-off JavaScript code in an isolated sandbox (Docker preferred) with optional dependencies, arguments, and timeout, without persisting a tool.

Instructions

Execute one-off Node.js code in the configured execution sandbox (Docker preferred, Node fallback) without persisting a tool

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": {
      "code": "<code>"
    },
    "name": "run_js_ephemeral"
  }
}

Input Schema

Name	Required	Description
`code`	Yes	JavaScript function body to execute inside export async function run(args) { ... }
`args`	No
`image`	No	Optional Docker image override
`dependencies`	No
`timeoutMs`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.4.1May 30, 2026

TDQS

A3.8/5.0

Behavior3/5

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

No annotations provided, so description carries full burden. It mentions execution sandbox (Docker preferred, Node fallback), but does not disclose error handling, side effects, or rate limits. Moderate disclosure.

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

Conciseness4/5

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

Single sentence front-loading the purpose, but could be slightly more informative without verbosity. No wasted words.

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

Completeness3/5

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

Given 5 parameters, nested objects, and no output schema, description lacks detail on return values, error handling, and constraints (e.g., code max length 200k). Adequate but not thorough.

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?

Schema coverage is 40%. Description adds value for code (function body inside async export) and dependencies (dependencies array with name/version), but not for args, image, or timeoutMs. Marginal improvement over schema.

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 clearly states 'Execute one-off Node.js code' with a specific verb and resource. It distinguishes from sibling tools by emphasizing ephemerality and not persisting a tool.

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 implies use for one-off execution via 'without persisting a tool', contrasting with dynamic.tool.* siblings for persistent tools. However, it lacks explicit when-to-use or when-not-to-use guidance.

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

Deploy Server