Mcp

Implements the Model Context Protocol over JSON-RPC 2.0. All operations go through a single POST /mcp endpoint, differentiated by the request body.

• Spec: modelcontextprotocol.io
• MIME: application/json
• Serializer: McpSerializer
• Routing: Body-matched (single endpoint)

Setup

import crate.protocols.mcp.policy;

auto crateRouter = router.crateSetup!Mcp;
crateRouter.add(userCrate);

Generated Tools

All operations use POST /mcp with a JSON-RPC body. The params.name field determines the operation:

Tool Name	Operation
list_users	List all
get_user	Get one
create_user	Create
replace_user	Replace
update_user	Update fields
delete_user	Delete

Request Format

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": "get_user",
    "arguments": { "id": "abc123" }
  },
  "id": 1
}

Base Operations

MCP registers additional protocol-level operations via onRouterInit:

Endpoint	Body Match	Purpose
POST /mcp	method: "initialize"	Protocol handshake
POST /mcp	method: "tools/list"	List available tools
GET /mcp/sse	—	Server-Sent Events stream
GET /.well-known/oauth-protected-resource	—	OAuth 2.1 metadata

The tools list is populated lazily via onRouterReady after all models are registered.

Not Yet Supported

• Resources: Only tools are exposed; no MCP resource endpoints
• Prompts: No prompt support
• Sampling: No sampling / LLM model endpoints
• Notifications: Server-to-client via SSE only; no client-initiated notifications
• Progress tracking: No progress reporting mechanism
• Logging: No structured logging API
• Cancellation: No request cancellation

Custom Base URL

auto crateRouter = router.crateSetup!(McpPolicy!(PolicyConfig("/tools")));
// Endpoint at POST /tools/mcp