OpenAPI to MCP Server Code Generator

import { Server } from "@modelcontextprotocol/sdk/server/index.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import { ListToolsRequestSchema, CallToolRequestSchema } from "@modelcontextprotocol/sdk/types.js";
import { z } from "zod";

const BASE_URL = process.env.API_BASE_URL || "https://petstore.swagger.io/v2";

const server = new Server(
  { name: "mcp-api-server", version: "1.0.0" },
  { capabilities: { tools: {} } }
);

// --- Expose MCP Tools ---
server.setRequestHandler(ListToolsRequestSchema, async () => ({
  tools: [
    {
      name: "findpetsbystatus",
      description: "Finds Pets by status",
      inputSchema: {
        type: "object",
        properties: {
          "status": { type: "string", description: "Status values that need to be considered for filter" },
        },
        required: ["status"],
      },
    },
    {
      name: "getpetbyid",
      description: "Find pet by ID",
      inputSchema: {
        type: "object",
        properties: {
          "petId": { type: "number", description: "ID of pet to return" },
        },
        required: ["petId"],
      },
    },
    {
      name: "deletepet",
      description: "Deletes a pet",
      inputSchema: {
        type: "object",
        properties: {
          "petId": { type: "number", description: "Pet id to delete" },
        },
        required: ["petId"],
      },
    },
  ],
}));

// --- Tool Execution Handlers ---
server.setRequestHandler(CallToolRequestSchema, async (request) => {
  const { name, arguments: args = {} } = request.params;

  const headers: Record<string, string> = {
    "Content-Type": "application/json",
    "User-Agent": "MCP-OpenAPI-Client/1.0",
  };

  switch (name) {
    case "findpetsbystatus": {
      let targetPath = `/pet/findByStatus`;
      const queryParams = new URLSearchParams();
      if (args.status !== undefined) queryParams.append("status", String(args.status));
      if (queryParams.toString()) targetPath += "?" + queryParams.toString();
      const response = await fetch(`${BASE_URL}${targetPath}`, { method: "GET", headers });
      const responseText = await response.text();
      return {
        content: [
          { type: "text", text: `HTTP Status: ${response.status}\n${responseText}` }
        ],
        isError: !response.ok,
      };
    }
    case "getpetbyid": {
      let targetPath = `/pet/${encodeURIComponent(String(args.petId ?? ""))}`;
      const response = await fetch(`${BASE_URL}${targetPath}`, { method: "GET", headers });
      const responseText = await response.text();
      return {
        content: [
          { type: "text", text: `HTTP Status: ${response.status}\n${responseText}` }
        ],
        isError: !response.ok,
      };
    }
    case "deletepet": {
      let targetPath = `/pet/${encodeURIComponent(String(args.petId ?? ""))}`;
      const response = await fetch(`${BASE_URL}${targetPath}`, { method: "DELETE", headers });
      const responseText = await response.text();
      return {
        content: [
          { type: "text", text: `HTTP Status: ${response.status}\n${responseText}` }
        ],
        isError: !response.ok,
      };
    }
    default:
      throw new Error(`Unknown tool: ${name}`);
  }
});

async function main() {
  const transport = new StdioServerTransport();
  await server.connect(transport);
  console.error("MCP OpenAPI Server listening over stdio...");
}

main().catch((err) => {
  console.error("Server error:", err);
  process.exit(1);
});