@chttp/mcp

Model Context Protocol server (JSON-RPC 2.0, spec revision 2025-06-18) authored in the scriptc-compilable subset — the same source type-checks to a JS package and lowers into a native ELF with scriptc build. Zero runtime dependencies. Validation flows through the Standard Schema seam, so @chttp/val, valibot, zod, or any conforming validator works; JSON Schema emission flows through a tiny adapter you inject.

import { Server, StreamableHttpTransport, tool } from "@chttp/mcp";
import * as v from "@chttp/val";

const server = new Server({
  name: "todo-mcp",
  version: "0.1.0",
  emitJsonSchema: (s) => v.toJsonSchema(s), // adapter seam — see docs/schema.md
});

tool(
  server,
  "add_todo",
  v.object({ text: v.pipe(v.string(), v.minLength(1)) }),
  async (input) => `added: ${input.text}`,
);

export default {
  fetch: StreamableHttpTransport.route(server), // (req) => Promise<Response>
};

What ships

• Server — tool/resource/prompt registration + handleRequest(JsonRpcRequest): Promise<JsonRpcResponse | null> covering the full method table (initialize, ping, tools/list, tools/call, resources/list, resources/read, resources/templates/list, prompts/list, prompts/get, notifications/*, logging/setLevel, completion/complete).
• StreamableHttpTransport — POST request/response + SSE GET ?stream=progress for notifications/progress, on the Request/Response surface. Mcp-Session-Id is set-but-unused in v1.
• The auto-wrap ladder for tool returns (string → text block, ContentBlock/ContentBlock[]/CallToolResult passthrough, plain object → dual content, null → empty, throw → isError).
• encodeSseEvent/encodeSseComment/encodeSseRetry, envelope helpers (parseBody, parseRequest, resultResponse, errorResponse, errorFor, notification), progress/log notification builders, runStdValidate/validatorFor.
• @chttp/mcp/client — a typed client on the ./client subpath: Client + toolDef/resourceDef/promptDef schema descriptors shared with server registration (server.toolDef(def, handler)), over FetchClientTransport, a node:net/node:tls HTTP/1.1+SSE transport for the ELF path, and StdioClientTransport (Node-only). See docs/client.md.

Docs: docs/ — integration, schema seams, transport, streamable-http coverage, auto-wrap, scriptc subset notes. Stdio wiring example: examples/integrations/mcp-stdio/.

Testing

pnpm --filter @chttp/mcp test      # node:test against the tsc build
bash packages/mcp/test/elf.test.sh # scriptc build + native smoke