mcp-kit: Cross-Runtime MCP Toolkit

The Problem

Building Model Context Protocol (MCP) servers today means choosing a runtime and getting locked in. Node.js servers don’t run on edge. Edge workers can’t do filesystem operations. Developers end up maintaining separate codebases for different deployment targets.

The Solution

mcp-kit keeps one server codebase portable across Node.js, Bun, Cloudflare Workers, Vercel Edge, and Netlify Edge. It uses Hono for the HTTP layer, runtime detection, and conditional feature loading.

Benchmark: Native Cold Start

Platform	Deployment	Cold Start (Native)
Node.js	Local (M1 Pro)	83ms
Bun	Local (M1 Pro)	111ms

mcp-kit uses Hono’s lightweight middleware model and keeps tool handler logic shared across runtimes. The point of the benchmark is not to crown a runtime; it is to keep startup cost visible while preserving portability.

Reproduction: To verify the baseline startup latency of these runtimes on your own machine:

1. Clone the Benchmark:

   git clone https://gist.github.com/omar391/da94c3ea15f5dc31e136cb33dca51b4a mcp-bench
   cd mcp-bench

2. Execute the Script:

   chmod +x mcp_bench.sh && ./mcp_bench.sh

Universal Runtime Abstraction

The core of mcp-kit is a runtime abstraction layer that detects the environment and swaps implementations for platform-specific capabilities (like fs vs. KV).

// Universal tool handler with runtime-aware capability detection
export const filesystemTool = defineTool({
  name: "read_file",
  handler: async (args, { runtime }) => {
    if (runtime.hasFilesystem) {
      return await runtime.fs.readFile(args.path);
    }
    // Transparently fall back to KV or S3 on edge
    return await runtime.storage.get(args.path);
  },
});

Key Features

• Runtime Support: Single codebase for Node.js, Bun, Cloudflare Workers, Vercel Edge, Netlify Edge
• Hono Framework: Lightweight HTTP framework chosen for fast startup and cross-runtime portability
• Cross-Runtime Compatibility: Runtime detection and conditional feature loading
• Type-Safe Tool Handlers: Strongly typed MCP tool definitions with validation
• Multi-Target Builds: Separate optimized builds for different runtime environments
• Multi-Instance Coordination: Version-aware upgrade flow for deployments

Architecture

I split universal features from local-only features, so edge deployments avoid filesystem/process code while local deployments can keep those capabilities.