Browser & edge compatible TypeScript SDK for Model Context Protocol

A fork of the official Model Context Protocol TypeScript SDK that works in Node.js, browsers, and edge runtimes.

The official @modelcontextprotocol/sdk was designed primarily for Node.js environments. When attempting to use it in:

• Browser environments (via bundlers like Webpack, Vite, esbuild)
• Cloudflare Workers (V8 isolates with Web APIs)
• Other edge runtimes (Deno Deploy, Vercel Edge Functions, etc.)

...you'll encounter errors due to Node.js-specific dependencies like:

• node:crypto (randomUUID, randomBytes)
• node:http (IncomingMessage, ServerResponse)
• node:stream (for stdio)
• node:child_process (for spawning processes)
• Third-party Node modules (raw-body, express, etc.)

This fork solves these compatibility issues while maintaining 100% API compatibility with the official SDK.

This fork systematically replaces Node.js-specific APIs with universal Web APIs, making the SDK work seamlessly in both Node.js and browser/edge environments.

src/server/sse.ts and src/server/streamableHttp.ts

• Replaced node:crypto with globalThis.crypto (Web Crypto API)
• Replaced node:http types with generic RequestLike/ResponseLike interfaces
• Replaced raw-body with request.text() for Fetch API and fallback stream reading for Node.js
• Added createSSESessionAdapter() function to create Fetch-compatible SSE sessions for edge runtimes

src/server/stdio.ts and src/client/stdio.ts

• Still Node.js-only (by design - stdio is inherently Node-specific)
• Made safe to import: detects runtime and throws descriptive errors in non-Node environments
• Uses globalThis.process instead of direct imports
• Lazy-loads Node-specific modules (cross-spawn, node:stream)

src/server/auth/handlers/register.ts

• Replaced crypto.randomBytes() with Web Crypto API
• Lazy-loaded Express dependencies (express, cors, express-rate-limit) for better tree-shaking
• Added runtime environment detection

src/shared/stdio.ts and related files

• Runtime-safe implementations that work in both Node.js and Web environments
• Proper type annotations for universal compatibility

Universal Transports

• SSEServerTransport: Works in Node.js, browsers, and edge runtimes
• StreamableHTTPServerTransport: Works in Node.js, browsers, and edge runtimes
• StdioServerTransport: Node.js only (safe to import, runtime-detected)

Edge Runtime Support

• Cloudflare Workers (V8 isolates)
• Deno Deploy
• Vercel Edge Functions
• Any environment with Web APIs

100% API Compatible

• Drop-in replacement for @modelcontextprotocol/sdk
• All official examples work unchanged
• Same imports, same API surface

npm install mcp-anywhere

Node.js 16.0.0+ (required for Web Crypto API)

• globalThis.crypto.randomUUID()
• globalThis.crypto.getRandomValues()

Browsers: Any modern browser with Web Crypto API support (all evergreen browsers)

Edge Runtimes: Cloudflare Workers, Deno Deploy, Vercel Edge Functions, etc.

Usage is exactly the same as the official SDK! All examples from the official documentation work without modification.

StdioServerTransport and StdioClientTransport still require Node.js. This is by design—stdio is fundamentally a Node.js concept (process.stdin/stdout, child processes).

import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js'; // Works in Node.js const transport = new StdioServerTransport(); // Throws clear error in browsers/edge runtimes: // "StdioServerTransport is only available in Node.js environments. // Use SSEServerTransport or StreamableHTTPServerTransport for browsers and edge runtimes."

For browsers and edge runtimes, use:

• SSEServerTransport / SSEClientTransport
• StreamableHTTPServerTransport / StreamableHTTPClientTransport

Tests use the same infrastructure as the official SDK:

# Run all tests npm test # Run specific test file npm test -- <test-file-pattern> # Run with coverage npm test -- --coverage

Integration tests verify that the refactored code works in both Node.js and simulated edge environments (using wrangler dev for Cloudflare Workers testing).

This fork maintains the same conditional exports as the official SDK:

{ "exports": { "./server/*": { "types": "./dist/server/*.d.ts", "default": "./dist/server/*.js" }, "./client/*": { "types": "./dist/client/*.d.ts", "default": "./dist/client/*.js" } } }

Node-specific peer dependencies (express, raw-body, cross-spawn) are marked as optional, so they won't cause installation failures in browser/edge environments.

For full MCP protocol documentation and usage examples, see:

• Official MCP Documentation
• Official TypeScript SDK
• MCP Specification

This fork implements the same APIs, so all official examples and documentation apply.

Issues and pull requests are welcome! Since this is a compatibility fork, contributions should:

1. Maintain 100% API compatibility with the official SDK
2. Use Web APIs instead of Node.js-specific APIs where possible
3. Include tests for both Node.js and edge runtime environments
4. Document any platform-specific behavior

This project is licensed under the MIT License—see the LICENSE file for details.

Upstream: modelcontextprotocol/typescript-sdk