Add Onyx MCP Sandbox to community servers list

[avd1729]

Description

Onyx is a secure MCP server for executing code inside Docker sandboxes. It supports multiple languages, including Python, Java, C, C++, JavaScript and Rust. The server provides the run_code tool with resource limits, isolated execution, and comprehensive tests.

Server Details

• Server: Onyx MCP Sandbox
• Changes to: Adding a new server reference with description, setup instructions, and repository link.

Motivation and Context

Adding Onyx provides the community with a multi-language code execution server that emphasizes security and isolation. It allows MCP clients to run arbitrary code safely in a sandboxed environment, filling a gap for safe, multi-language execution servers.

How Has This Been Tested?

• Tested with local MCP client (sandbox_server) on Windows and Linux.
• All executors for Python, Java, C, C++, JavaScript and Rust have corresponding unit tests under tests/.
• Verified correct output and proper resource isolation in Docker.

Breaking Changes

• None. Adding a new server reference does not affect existing servers or MCP client configurations.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Protocol Documentation
• My changes follow MCP security best practices
• I have updated the server's README accordingly
• I have tested this with an LLM client
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have documented all environment variables and configuration options

Additional context

• The server is designed to be extendable; new languages can be added by implementing new executors.
• Docker images for each language should be pre-pulled for faster execution.
• Full setup and integration instructions are in the Onyx README.