Transport Modes

The server supports 4 transport modes for different use cases.

Stdio (Default)

velocity_mcp --mode stdio

JSON-RPC v2.0 over stdin/stdout. Compatible with all MCP clients.

• Reader thread + channel architecture (stdin reads never block shutdown)
• Full MCP spec compliance: ping, logging/setLevel, notifications/cancelled
• Cursor pagination on tools/list
• Graceful shutdown via atomic flag

HTTP/SSE

velocity_mcp --mode http --addr 0.0.0.0:3000

Full HTTP transport via Axum:

Endpoint	Description
/mcp	JSON-RPC over HTTP POST
/mcp/stream	Streamable HTTP with SSE response
/mcp/batch	Batch JSON-RPC
/sse	SSE for real-time streaming
/ws	WebSocket upgrade
/health	Health check
/performance	Performance metrics (JSON)
/metrics	Prometheus metrics
/sessions	Session management

Features: session management (up to 1000), API key auth, CORS, TLS/HTTPS, request size limits.

WebSocket

velocity_mcp --mode ws --addr 0.0.0.0:3000

Dedicated WebSocket transport for bidirectional real-time communication.

Shared Memory

velocity_mcp --mode shmem --buffer-path nmcp_buffer.bin

Memory-mapped file IPC for ultra-low latency. Two wire formats with auto-detection:

NDA-native (binary):

[4B: "NMCP"] [32B: Merkle root] [1B: method type] [TLV: data]

JSON-RPC (backwards-compatible): Standard JSON-RPC strings.

Buffer: 64KB (4KB input + 61KB output). Win32 Events on Windows for zero-poll blocking.

Performance: 12.7M req/s at 8 threads (NDA-native).

See also: Getting-Started, Performance, Configuration