OpenServer

A Bun framework for building MCP servers. Connects to any MCP client — Claude Code, Cursor, custom agents — and gives them a live local backend they can extend at runtime.

One call spins up an MCP server (stdio + HTTP/SSE), a REST API, WebSocket live reload, and a filesystem-backed database:

import { createServer, defineSchema } from "openserver";

const tasks = defineSchema({ name: "task", fields: { title: "string", done: "boolean" } });
const server = createServer({ schemas: [tasks] });
await server.start();

CRUD tools, REST routes, and HTML views are auto-generated from schemas. The agent can also extend the server itself at runtime via meta-tools (create_tool, create_view, create_schema).

Who is this for: developers who want an AI agent to build and operate a real local backend without manual scaffolding.

Requires Bun v1.0+.

Scaffold a full project with the CLI:

npx create-openserver my-app
cd my-app
bun run dev

Point any MCP client at the project and start describing what you want to build.

Install the package:

bun add openserver

Create a server.ts:

import { createServer, defineSchema } from "openserver";

const tasks = defineSchema({
  name: "task",
  fields: { title: { type: "string", required: true }, done: { type: "boolean" } },
});

const server = createServer({ schemas: [tasks], transport: "http", port: 3000 });
await server.start();

Run it:

bun run server.ts

The server exposes MCP over HTTP at http://localhost:3000/mcp, REST routes under /api/tasks, and a view at /tasks.

Returns { start(): Promise<void> }.

Auto-generates for each schema:

• MCP tools: create_<name>, read_<name>, list_<name>s, update_<name>
• REST routes: GET/POST /api/<name>s, GET/PUT/DELETE /api/<name>s/:slug
• HTML view: /<name>s

Shorthand: a bare string ("string", "boolean", etc.) is also accepted as a field value.

interface CustomToolDef {
  name: string;
  description?: string;
  inputSchema: Record<string, ZodType>; // Zod shape (not a JSON object)
  handler: (args: any) => Promise<any>;
}

• create_tool — generates a new MCP tool with handler and input schema
• create_view — writes an HTML view served at /<name>
• create_schema — creates a Zod schema and registers CRUD tools for it
• list_tools — lists all registered tools and their current status

MIT