MCP Streamable HTTP Server Template

What is this?

A template for building MCP servers. Clone it, strip what you don't need, wire your API client, define tools. It's designed to be readable and easy to build on.

Ships with dual-runtime support (Node.js and Cloudflare Workers from the same codebase), five auth strategies, encrypted token storage, and pretty much everything the latest MCP spec supports.

What is MCP?

Model Context Protocol is a JSON-RPC 2.0 wire protocol where servers expose typed capabilities (tools for actions, resources for data, prompts for templates) and clients (IDEs, agents, chat apps) invoke them based on LLM decisions.

Neither side implements the other's logic: servers know nothing about which LLM uses them, clients know nothing about how tools work internally. This decoupling solves the N×M integration problem. One server serves any compliant client, one client consumes any compliant server.

What's supported?

Feature	Node.js	Workers	Notes
Tools (list, call)	✅	✅	Core capability, both runtimes
Resources (list, read, templates)	✅	✅	Static and dynamic resources
Prompts (list, get)	✅	✅	Template-based prompt generation
Progress notifications	✅	✅	Long-running tool feedback
Cancellation	✅	✅	AbortSignal-based
Pagination	✅	✅	Cursor-based for large lists
Logging	✅	✅	Server→client log messages
Sampling (server→client LLM)	✅	❌	Requires persistent SSE stream
Elicitation (user input)	✅	❌	Requires persistent SSE stream
Roots (filesystem access)	✅	❌	Requires client capability check

Protocol versions supported: 2025-11-25, 2025-06-18, 2025-03-26, 2024-11-05.

Getting started

First, generate an encryption key (you'll need this for both runtimes):

openssl rand -base64 32 | tr -d '=' | tr '+/' '-_'

Node.js

bun install
cp .env.example .env          # Configure PROVIDER_*, AUTH_*, OAUTH_* vars
                              # Set RS_TOKENS_ENC_KEY with generated key
bun dev                       # MCP: localhost:3000/mcp, OAuth: localhost:3001

Cloudflare Workers

bun install
wrangler kv:namespace create TOKENS                    # Note the ID
# Update wrangler.toml with KV namespace ID

wrangler secret put PROVIDER_CLIENT_ID
wrangler secret put PROVIDER_CLIENT_SECRET
wrangler secret put RS_TOKENS_ENC_KEY                  # Paste generated key

wrangler dev                  # Local: localhost:8787/mcp
wrangler deploy               # Production: your-worker.workers.dev/mcp

Server endpoints

Endpoint	Method	Purpose
/mcp	POST, GET, DELETE	MCP protocol (JSON-RPC)
/health	GET	Health check + readiness
/.well-known/oauth-authorization-server	GET	OAuth AS metadata
/.well-known/oauth-protected-resource	GET	Protected resource metadata
/authorize	GET	Start OAuth flow
/oauth/callback	GET	Provider redirect target
/token	POST	Token exchange
/register	POST	Dynamic client registration
/revoke	POST	Token revocation

Discovery endpoints also available under /mcp/.well-known/* prefix.

Node.js vs Cloudflare Workers

The template produces two runtimes from the same codebase. Here's what you need to know:

Node.js (Hono + @hono/node-server)

• Entry: src/index.ts
• Transport: SDK's StreamableHTTPServerTransport
• Sessions: MemorySessionStore (default) or SqliteSessionStore for persistence
• Full MCP features including bidirectional requests (sampling, elicitation, roots)
• Local development: bun dev

Cloudflare Workers

• Entry: src/worker.ts
• Transport: Custom JSON-RPC dispatcher (shared/mcp/dispatcher.ts)
• Sessions: KvSessionStore with memory fallback (persists across requests)
• Request→response only; no server-initiated messages
• Deploy: wrangler deploy

Shared code lives in src/shared/ (tools, storage interfaces, OAuth flow, utilities). Runtime-specific adapters live in src/adapters/http-hono/ and src/adapters/http-workers/.

When to use which:

• Node.js: Local development, full MCP features, self-hosted servers
• Workers: Production deployment, global edge, simple tool wrappers

Authorization

Naming conventions (important!)

Use generic PROVIDER_* names, not service-specific names. This keeps the template portable and configuration consistent across all MCP servers.

✅ Correct	❌ Wrong
PROVIDER_CLIENT_ID	SPOTIFY_CLIENT_ID, LINEAR_CLIENT_ID
PROVIDER_CLIENT_SECRET	SPOTIFY_CLIENT_SECRET, GMAIL_SECRET
PROVIDER_ACCOUNTS_URL	SPOTIFY_ACCOUNTS_URL
PROVIDER_API_URL	LINEAR_API_URL, GITHUB_API_URL

Why?

• Same env var names work across all servers (Spotify, Linear, Gmail, etc.)
• Deployment scripts don't need service-specific logic
• .env.example and wrangler.toml remain generic templates
• Easier to audit security (one pattern to check)

Example .env:

# Generic provider config — same vars for any OAuth provider
PROVIDER_CLIENT_ID=your-client-id
PROVIDER_CLIENT_SECRET=your-client-secret
PROVIDER_ACCOUNTS_URL=https://accounts.spotify.com   # or github.com, etc.
PROVIDER_API_URL=https://api.spotify.com             # optional, for API calls

Exception: If a server integrates multiple providers simultaneously (rare), prefix with provider name: GITHUB_CLIENT_ID, GITLAB_CLIENT_ID. Single-provider servers should always use PROVIDER_*.

Auth strategies

Five auth strategies, configured via AUTH_STRATEGY env var:

Strategy	Header	Use Case
oauth	Authorization: Bearer <RS_TOKEN>	Full OAuth 2.1 PKCE flow with RS token → provider token mapping
bearer	Authorization: Bearer <TOKEN>	Static token from BEARER_TOKEN env
api_key	X-Api-Key: <KEY> (configurable)	Static key from API_KEY env
custom	Multiple headers	Custom headers from CUSTOM_HEADERS env
none	—	No authentication

OAuth flow (strategy=oauth):

1. Client discovers AS metadata via /.well-known/oauth-authorization-server
2. Client initiates PKCE flow → /authorize → provider login
3. Provider callback → server issues RS tokens (access + refresh)
4. Client sends RS token → server maps to provider token → tool executes with provider API

Token storage (RS token → provider token mapping):

• FileTokenStore — Node.js, file-based with optional encryption
• MemoryTokenStore — Both runtimes, in-memory with TTL
• KvTokenStore — Workers, Cloudflare KV with optional encryption
• All support AES-256-GCM encryption via RS_TOKENS_ENC_KEY

Sessions

Sessions enable multi-tenant operation. One server instance can serve multiple users with isolated state. Both runtimes use SessionStore for this.

What sessions give you:

• API key → session binding (who owns this connection)
• Session limits per API key (default: 5, LRU eviction)
• Session validation on every request (404 for invalid/expired sessions)
• Protocol version tracking per session
• Server→client request routing (sampling/elicitation need to know which client)

What sessions don't give you (that's on the agent):

• Conversation memory ("reply to that email")
• Workflow state (draft continuation, last issue ID)
• Context carryover between tool calls

Storage implementations:

Store	Runtime	Backend	Persistence
MemorySessionStore	Both	In-memory Map	Process lifetime
SqliteSessionStore	Node.js	SQLite via Drizzle	Disk
KvSessionStore	Workers	Cloudflare KV	Global

Session lifecycle (per MCP spec):

1. Client sends initialize request without Mcp-Session-Id header
2. Server creates session via SessionStore.create(sessionId, apiKey), returns session ID in response header
3. Client sends initialized notification with Mcp-Session-Id → server marks session as initialized
4. All subsequent requests must include Mcp-Session-Id (400 Bad Request if missing)
5. Server validates session exists on every request (404 Not Found if invalid/expired)
6. Session expires after TTL (default: 24h) or client sends DELETE request

API key resolution (for session binding):

• X-Api-Key or X-Auth-Token header (direct API key auth)
• Bearer token from Authorization header (OAuth RS token)
• Static API_KEY from config (fallback)
• "public" (unauthenticated)

Multi-tenant model:

User A (api_key_1) ──┐
                     │
User B (api_key_2) ──┼──▶ Single MCP Server ──▶ Provider API
                     │    (sessions isolate users)
User C (api_key_3) ──┘

Adding tools

Location: src/shared/tools/

Pattern: schema → metadata → handler → register

// 1. Define input schema with Zod
export const myToolInputSchema = z.object({
  query: z.string().describe('Search query'),
});

// 2. Create tool with defineTool()
export const myTool = defineTool({
  name: 'my_tool',
  title: 'My Tool',
  description: 'What it does',
  inputSchema: myToolInputSchema,
  outputSchema: { result: z.string() },  // optional
  annotations: {
    readOnlyHint: true,
    destructiveHint: false,
  },
  handler: async (args, context) => {
    // 3. Implement handler
    return {
      content: [{ type: 'text', text: args.query }],
      structuredContent: { result: args.query },  // required if outputSchema defined
    };
  },
});

// 4. Add to sharedTools array in registry.ts
export const sharedTools: RegisteredTool[] = [
  asRegisteredTool(healthTool),
  asRegisteredTool(echoTool),
  asRegisteredTool(myTool),  // ← add your tool here
];

Annotations control how clients display/invoke: readOnlyHint, destructiveHint, idempotentHint, openWorldHint.

Services: For complex integrations, put business logic in src/shared/services/. Extract when: handler exceeds ~30 lines, multiple tools share logic, or external API needs rate limiting/retries. Simple tools can keep logic inline.

Known limitations

Node.js runtime — Full MCP support including server→client requests (sampling, elicitation, roots) via SDK's StreamableHTTPServerTransport. Sessions persist via MemorySessionStore (default) or SqliteSessionStore for disk persistence.

Cloudflare Workers runtime — Request→response mode only. Sessions persist via KvSessionStore across requests, but transport state is stateless (no SSE streams). Server→client requests (sampling, elicitation, roots) aren't available because they require an active SSE stream which Workers can't maintain. Use Workers for simple tool servers; for full MCP features, use Node.js or implement Durable Objects.

License

MIT