E2B MCP Server

execute_javascript

Execute JavaScript code in an isolated E2B sandbox for secure testing and scripting. Optionally target a specific sandbox by ID.

Instructions

Execute JavaScript/Node.js code in an E2B sandbox environment

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": "execute_javascript"
  }
}

Input Schema

Name	Required	Description	Default
`code`	Yes	JavaScript code to execute
`sandbox_id`	No	Optional sandbox ID to use specific sandbox

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Aug 30, 2026

TDQS

B3.1/5.0

Behavior2/5

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

No annotations are present, so the description carries the full burden of behavioral disclosure. It only mentions the sandbox environment and does not state whether execution returns output, how stdout/stderr are handled, whether state persists, or what side effects may occur. This leaves the agent guessing about execution semantics.

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?

The description is a single, front-loaded sentence with no waste. It efficiently conveys the core operation and environment, though it sacrifices helpful context for brevity.

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

Completeness2/5

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

With no output schema and no annotations, the description should clarify what the caller receives and how the sandbox behaves. It omits return format, timeout behavior, and environmental constraints, making it insufficient for confident invocation beyond passing arbitrary code.

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 description coverage is 100%, so the input schema already documents both parameters and their purpose. The description adds no additional semantic value beyond what the schema provides, meeting the baseline for a fully documented 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 states a specific verb ('Execute'), a specific resource ('JavaScript/Node.js code'), and a specific environment ('E2B sandbox'). This clearly distinguishes the tool from its sibling execute_python by language and from file operations, leaving no ambiguity about what resource it acts on.

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

Usage Guidelines2/5

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

The description gives no guidance on when to prefer this tool over execute_python or when not to use it. There are no exclusions, prerequisites, or alternative routing hints. Usage must be inferred entirely from the tool name and description.

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

Deploy Server