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Overview
A thin, secure bridge from Elysia HTTP routes to Model Context Protocol.
@mwillbanks/elysia-mcp-adapter adds a Model Context Protocol HTTP endpoint to an Elysia application. Existing routes can become MCP tools, while explicit registration methods cover MCP-only tools, resources, resource templates, and prompts.
Preserve the Elysia lifecycle
Route-backed calls are converted into an internal Request and sent through app.handle(). This keeps the behavior that already protects and shapes your HTTP API:
- request parsing and TypeBox validation
- local hooks, guards, and authentication plugins
- error handlers and response mapping
- route-specific status codes and headers
The adapter never calls an Elysia route handler directly.
A focused MCP surface
| Primitive | Route-backed | Standalone | Default exposure |
|---|---|---|---|
| Tools | Yes | .mcpTool() | Eligible HTTP routes become tools |
| Resources | Yes | .mcpResource() | Explicit opt-in |
| Resource templates | Yes | .mcpResource() | Explicit opt-in |
| Prompts | Yes | .mcpPrompt() | Explicit opt-in |
The transport lives at POST /mcp by default and implements initialization, discovery, tool calls, resource reads, and prompt retrieval over JSON-RPC.
Design principles
- Elysia remains the application framework. The adapter translates protocols instead of introducing a parallel runtime.
- JSON Schema stays JSON Schema. Route schemas are sanitized for transport without a TypeBox-to-Zod translation layer.
- Exposure is deliberate. Tools are convenient by default; resources, prompts, headers, browser origins, and binary output require explicit configuration.
- Existing integrations keep working. OpenAPI metadata, auth plugins, hooks, guards, error handling, and OpenTelemetry remain in the Elysia lifecycle.