VERIFIED

JS

Safety: 55/100

0.0(0)

Executes JavaScript code in a V8 engine with optional heap persistence via S3 or local storage, offering flexible integration with AI agents.

MCP ServersFreemium

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Overview

Executes JavaScript code in a V8 engine with optional heap persistence via S3 or local storage, offering flexible integration with AI agents.

The server's safety depends on the chosen mode and storage. Stateless mode is safer due to its ephemeral nature. Stateful mode, especially with S3, requires careful credential management and awareness of the risks associated with persistent JavaScript execution.

Performance is dependent on the complexity of the JavaScript code. Stateful mode may have slower initial execution due to heap snapshot loading.

Cost is primarily related to the compute resources used to run the V8 engine. S3 storage costs may apply if heap snapshots are stored in S3.

HybridRust28 stars0BSDReleased 10/17/2025CI/CD

Connections & Capabilities

Connects To

FilesystemAWSS3

Capabilities

ExecReadWrite

Client Compatibility

Claude Desktop

full

Cursor

full

Windsurf

untested

VS Code (Copilot)

untested

Quickstart

Claude Desktop Config

{
  "mcpServers": {
    "js": {
      "command": "/usr/local/bin/mcp-v8 --s3-bucket my-bucket-name"
    }
  }
}

Tools (1)

high

JavaScript Execution

Executes arbitrary JavaScript code within a V8 engine.

Unrestricted code execution can lead to various security risks.

Security

Auth Method

None

Data Locality

hybrid

Known Risks

!Potential for code injection attacks via JavaScript execution.
!Exposure of AWS credentials if S3 storage is used improperly.
!Denial-of-service if JavaScript code consumes excessive resources.
!State persistence in stateful mode could lead to security vulnerabilities if not properly managed.

Safety Score

moderate risk

Positive

+V8 engine provides a degree of isolation.
+Stateless mode eliminates persistent state risks.
+Clear limitations on available JavaScript APIs (no network, file system access).
+Heap snapshots can be stored locally or in S3, allowing for controlled persistence.

Risks

-Arbitrary JavaScript execution poses inherent risks.
-Stateful mode introduces potential for persistent malicious code.
-S3 storage requires careful management of AWS credentials.
-Lack of `async/await` could lead to blocking operations.

Use Cases

Data Transformation

-Transforming data from one format to another.
-Filtering and cleaning data.
-Performing calculations on data.

Code Generation

-Generating code snippets based on input.
-Creating templates for code generation.
-Automating repetitive coding tasks.

Mathematical Computation

-Performing complex mathematical calculations.
-Simulating physical systems.
-Solving equations and optimization problems.

Text Processing

-Extracting information from text.
-Summarizing text.
-Translating text.

Who Is This For?

Best For

AI agents needing to execute JavaScript code.
Scenarios requiring data transformation or code generation.
Prototyping and experimentation with JavaScript code.
Tasks where state persistence is beneficial (with caution).

Not Ideal For

Applications requiring network access or file system access.
Long-running or asynchronous tasks.
Security-critical applications without careful sandboxing and validation.

Autonomy & Execution

Default ModeConfigurable

Sandboxed

The level of autonomy depends on how the tool is used within the agent. The V8 engine provides some sandboxing, but careful consideration should be given to the code being executed.

StatelessYes

Retry LogicNone

ConcurrencySingle-threaded

Production Tip

Use stateless mode in production environments where persistence is not required to minimize security risks.

FAQ

What are the limitations of the JavaScript environment?

The environment lacks `async/await`, network access, file system access, and external package support.

How do I persist state between runs?

Use stateful mode with either S3 or local filesystem storage.

Is the JavaScript code sandboxed?

The V8 engine provides some sandboxing, but it's not a fully isolated environment. Exercise caution.

Can I use `console.log` for debugging?

No, `console.log` output is not captured. Return the value you want to inspect as the last line of your code.

What is the difference between stateless and stateful mode?

Stateless mode starts with a fresh V8 isolate each time, while stateful mode persists the heap state between executions.

How do I configure the server for S3 storage?

Use the `--s3-bucket <bucket>` command line argument and ensure AWS credentials are in your environment.

What happens if I provide multiple storage options?

The server will return an error. Only one storage option can be used at a time.

Key Features

V8 JavaScript Runtime - Provides a high-performance, industry-standard engine for executing complex logic.

MCP Protocol Compliance - Enables seamless integration with modern AI development environments like Claude and Cursor.

Heap Persistence - Allows saving and restoring the runtime state to ensure continuity across agent tasks.

S3 Storage Integration - Offers scalable cloud-based persistence for heap snapshots.

Local Filesystem Support - Enables offline or local development workflows with persistent state storage.

Sandboxed Execution - Provides a secure, isolated environment for running arbitrary AI-generated code.

Use Cases & Problems Solved

Use Cases

•Use when you need to execute complex data transformations or business logic within an AI agent's workflow without external API dependencies.
•Perfect for building stateful AI agents that require memory across multiple interactions by leveraging persistent heap snapshots.
•Ideal if you need to perform secure, sandboxed JavaScript calculations directly within the Claude or Cursor development environments.
•Great for developers who need to integrate custom JavaScript utilities into LLM-driven pipelines while maintaining state between execution steps.
•Use when prototyping server-side logic in an isolated environment that can be easily backed up or synced to S3 storage.
•Perfect for offloading heavy JavaScript computations from an LLM prompt to a dedicated V8 runtime to reduce token usage and improve accuracy.

Problems Solved

✓Eliminates the risk of non-deterministic or hallucinated code execution by using a verified V8 runtime.
✓Removes the limitation of stateless LLM interactions by providing persistent heap storage for long-running agent tasks.
✓Solves the security concerns of running arbitrary AI-generated code by isolating it within a controlled MCP server environment.
✓Reduces the complexity of managing external microservices by allowing direct script execution via the MCP protocol.

Who It's For

AI software engineers building agentic workflowsFull-stack developers integrating LLMs into existing web applicationsOpen-source contributors developing extensions for Claude or CursorDevOps engineers managing sandboxed execution environments for AI modelsPrototyping teams building complex stateful automation scripts

Metrics

Discovered2/14/2026

Reviews0

Saved By0 users

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