MCP Server Handler

The MCP (Model Context Protocol) Server handler allows you to run a lightweight, stateless MCP server on your gateway that automatically transforms your API routes into MCP tools.

This enables your API gateway to seamlessly serve external AI tools and agents through Model Context Protocol interactions by using your existing APIs, without needing to duplicate functionality or rebuild business logic in your backend.

Each MCP Server handler has a 1:1 relationship with a route. That means one route can host one server. A gateway may have any number of MCP servers.

A single MCP server may have many tools and prompts, where each tool interfaces with an API route in your gateway. You can compose multiple MCP servers on different routes to tailor MCP tools and prompts for each server's specific purpose.

The MCP Server Handler works by re-invoking configured routes on the gateway. It does not go back out to HTTP: it keeps requests within the gateway while still re-invoking the policy pipeline for your routes. This means that if you configure an MCP server with policies, routes with policies, and configure those routes as tools, the policy pipelines for both will be invoked. First the MCP server handler inbound policies, then the inbound policies for the tool's route, then the outbound policies for the tool's route, and finally, the outbound policies for the MCP server handler.

Setup via Portal

Open the Route Designer by navigating to the Files tab, then click routes.oas.json. For any route definition, select MCP Server from the Request Handlers drop-down. Set the method to POST.

Configure the handler with the following required options:

• Server Name - The name of the MCP server. AI MCP clients will read this name when they initialize with the server.
• Server Version - The version of your MCP server. AI MCP clients read this version when they initialize with the server and may make autonomous decisions based on the versioning of your MCP server and the instructions they've been given.

Next, configure your routes to be transformed into MCP tools or prompts (see Configuration section below).

Setup via routes.oas.json

The MCP Server handler can be manually added to the routes.oas.json file with the following route configuration:

Code
 
"paths": {
  "/mcp": {
    "x-zuplo-path": {
      "pathMode": "open-api"
    },
    "post": {
      "summary": "MCP Server",
      "x-zuplo-route": {
        "corsPolicy": "none",
        "handler": {

          // The MCP Server Handler handler
          // and required options

          "export": "mcpServerHandler",
          "module": "$import(@zuplo/runtime)",
          "options": {
            "name": "example-mcp-server",
            "version": "1.0.0",
            "debugMode": false,
          }
        },
        "policies": {
          "inbound": []
        }
      }
    }
  }
}

Configuration

The MCP Server handler requires the following configurations:

• name (optional) - The name identifier of the MCP server.
• version (optional) - The version of the MCP server.
• debugMode (optional, default false) - Verbose logs on server startup, initialization, tool listing, and tool calls. NOT recommended for production environments.
• operations - An array of operation references to register with the MCP server. Each operation can be a tool, prompt, or resource based on its x-zuplo-route.mcp configuration.

MCP 2025-06-18 Global Options

• includeOutputSchema (optional, default: false) - Whether to include output schema from the route's OpenAPI response schema. When true, the schema from successful responses (2xx) will be used as outputSchema for MCP tools.
• includeStructuredContent (optional, default: false) - Whether to include structured content in responses. When true, response JSON will be parsed and included as structuredContent. When false, only text content will be returned.

Operations

Configure MCP tools, prompts, and resources using the operations configuration. Specify OpenAPI files and the exact operation IDs you want to expose:

Code
 
"paths": {
  "/mcp": {
    "post": {
      "x-zuplo-route": {
        "handler": {
          "export": "mcpServerHandler",
          "module": "$import(@zuplo/runtime)",
          "options": {
            "name": "My MCP Server",
            "version": "1.0.0",
            "operations": [
              {
                "file": "./config/weather.oas.json",
                "id": "getCurrentWeather"
              },
              {
                "file": "./config/todos.oas.json",
                "id": "createTodo"
              }
            ]
          }
        }
      }
    }
  }
}

• file: Path to an OpenAPI JSON spec file (relative to the project root)
• id: The specific operation ID to include from the targeted file

This approach provides explicit control over exactly which API operations become MCP tools, prompts, or resources.

Deprecated Configurations

Code
 
"post": {
  "operationId": "mcp-server",
  "x-zuplo-route": {
    "handler": {
      "export": "mcpServerHandler",
      "module": "$import(@zuplo/runtime)",
      "options": {
        "files": [
          {
            "path": "./config/weather.oas.json",
            "operationIds": [
              "getCurrentWeather"
            ]
          }
        ],
        "prompts": [
          {
            "path": "./config/weather.oas.json",
            "operationIds": [
              "weatherPrompt"
            ]
          }
        ]
      }
    }
  }

MCP Tools

Tools are the main way that AI agents can discover capabilities from MCP servers. They are flexible, lite weight ways to execute some functionality, query some data, or perform an action on the user's behalf.

Routes configured as MCP prompts may include the x-zuplo-route.mcp extension with type: "tool" in their OpenAPI definition. By default, without the x-zuplo-route.mcp configuration, the MCP server handler will assume the provided operation is a "tool". See MCP Server Tools for detailed documentation.

Custom MCP Tools

Create custom tools as routes with full programmatic control using dedicated OpenAPI specifications and custom handler functions.

This approach provides maximum flexibility for complex workflows. See MCP Server Custom Tools for detailed documentation.

MCP Prompts

In addition to tools, MCP servers can expose prompts - reusable, parameterized prompt templates that AI clients can request and execute. Configure prompts using the operations array in your MCP server options, just like tools.

Routes configured as MCP prompts must include the x-zuplo-route.mcp extension with type: "prompt" in their OpenAPI definition. See MCP Server Prompts for detailed documentation.

MCP Resources

MCP servers can also expose resources - static read-only content like documentation, configuration files, or any other data an AI system might need. Like tools and prompts, configure resources using the operations array in your MCP server options.

Routes configured as MCP resources must use the GET method and must include the x-zuplo-route.mcp extension with type: "resource" in their OpenAPI definition.

See MCP Server Resources for detailed documentation.

Route x-zuplo-route.mcp configuration

You can customize individual tools, prompts, and resources using the x-zuplo-route.mcp property in your OpenAPI definition. This allows you to define the type of MCP capability and provide specific metadata.

Code
 
"paths": {
  "/weather/current": {
    "get": {
      "operationId": "getCurrentWeather",
      "summary": "Get current weather",
      "x-zuplo-route": {
        "handler": { ... },
        "mcp": {
          "type": "tool",
          "name": "get_current_weather",
          "description": "Retrieve current weather conditions for a specified location",
          "enabled": true
        }
      }
    }
  },
  "/prompts/greeting": {
    "post": {
      "operationId": "greeting-prompt",
      "x-zuplo-route": {
        "handler": { ... },
        "mcp": {
          "type": "prompt",
          "name": "greeting_generator",
          "description": "Generate a personalized greeting"
        }
      }
    }
  }
}

Common options:

• type: The type of MCP capability (tool, prompt, resource, or graphql). Defaults to tool if not specified.
• name: Override the name shown to AI systems (defaults to operationId)
• description: Override the description for AI consumption (defaults to route description/summary)
• enabled: Whether this operation should be available in the MCP server.

See the respective tools, prompts and resources documentation for type-specific options.

Authentication

OAuth Authentication

The MCP Protocol natively supports OAuth authentication to enable MCP Clients to authenticate and authorize themselves when calling tools. For more information, see the official MCP Authentication documentation.

Zuplo allows you to configure any of the built-in OAuth policies (like Auth0, Okta, etc.) on the MCP Server route to secure it. To enable OAuth authentication, you will need to have an OAuth Authorization server configured. Specifically, the OAuth Authorization server will need to support the following things:

1. (Optional but recommended) OAuth 2.0 Dynamic Client Registration
2. Authorization Code Grant with PKCE
3. Refresh Tokens

For an example of a basic configuration of an Authorization Server with Auth0, see: Setting up Auth0 as an Authentication Server for MCP OAuth Authentication.

Once you have configured your authorization server, you can do the following to enable OAuth authentication on your MCP Server:

1. Create an OAuth policy on your MCP Server route. This policy will need to have the option "oAuthResourceMetadataEnabled": true, for example:

   Code
    
   {
     "name": "mcp-oauth-inbound",
     "policyType": "oauth-inbound",
     "handler": {
       "export": "Auth0JwtInboundPolicy",
       "module": "$import(@zuplo/runtime)",
       "options": {
         "auth0Domain": "my-auth0-domain.us.auth0.com",
         "audience": "https://my-mcp-audience",
         "oAuthResourceMetadataEnabled": true
       }
     }
   }

   In this example, the audience should be the identifier of the Auth0 API you want your MCP Server to be protected by. For more information on configuring OAuth JWT policies, see the OAuth Policy docs.

2. Add the OAuth policy to the MCP Server route. For example:

   Code
    
   "paths": {
     "/mcp": {
       "post": {
         "x-zuplo-route": {
           // etc. etc.
           // other properties and route handlers for MCP
   
           "policies": {
             "inbound": [
               "mcp-oauth-inbound"
             ]
           }
         }
       }
     }
   }

3. Add the OAuthProtectedResourcePlugin to your runtimeInit function in the zuplo.runtime.ts file:

   Code
    
   import { OAuthProtectedResourcePlugin } from "@zuplo/runtime";
   
   export function runtimeInit(runtime: RuntimeExtensions) {
     runtime.addPlugin(
       new OAuthProtectedResourcePlugin({
         authorizationServers: ["https://your-auth0-domain.us.auth0.com"],
         resourceName: "My MCP OAuth Resource",
       }),
     );
   }

   See the OAuth Protected Resource Plugin docs for more details.

API Key Auth

An MCP server on Zuplo can be configured to use an API key from a query parameter using the Query Parameter to Header Policy.

Configure the policy to expect a query param and inject it as an Auth header:

Code
 
{
  "policies": [
    {
      "name": "mcp-query-param-to-header-inbound",
      "policyType": "query-param-to-header-inbound",
      "handler": {
        "export": "QueryParamToHeaderInboundPolicy",
        "module": "$import(@zuplo/runtime)",
        "options": {
          "queryParam": "apiKey",
          "headerName": "Authorization",
          "headerValue": "Bearer {value}"
        }
      }
    }

    // etc. etc. other policies, your API key policy
  ]
}

Then, to secure your MCP endpoint, add the "query param to header" policy before your API key policy:

Code
 
{
  "paths": {
    "/mcp": {
      "post": {
        "x-zuplo-route": {
          // etc. etc.
          // other properties and route handlers for MCP

          "policies": {
            "inbound": [
              "mcp-query-param-to-header-inbound",
              "api-key-auth-inbound"
            ]
          }
        }
      }
    }
  }
}

Will will effectively transform the query param into a Authorization: Bearer header and pass those through to other routes on your gateway.

Then, when using MCP clients, simply add your API key as a query param! For example, in Cursor:

Code
 
{
  "mcpServers": {
    "my-zuplo-mcp-server": {
      "url": "https://my-server.zuplo.com/mcp?apiKey=123abc"
    }
  }
}

Testing

MCP Inspector

Use the MCP Inspector, a developer focused tool for building MCP servers, to quickly and easily test out your MCP server:

Code
 
npx @modelcontextprotocol/inspector

By default, this will start a local MCP proxy and web app that you can use on localhost to connect to your server, list tools, call tools, view message history, and more.

To connect to your remote Zuplo MCP server in the Inspector UI:

1. Set the Transport Type to "Streamable HTTP"
2. Set the URL to your Zuplo gateway with the route used by the MCP Server Handler (that is, https://my-gateway.zuplo.dev/mcp)
3. If you have configured OAuth authentication, you will need to login using the OAuth flow using the Open Auth Settings button.
4. Hit Connect.

Curl

For more fine grained debugging, utilize MCP JSON RPC 2.0 messages directly with curl. There are lots of different interactions and message flows supported by MCP, but some useful ones include:

Ping

To send a simple "ping" message, which can be useful for testing availability of your MCP server:

Code
 
curl https://my-gateway.zuplo.dev/mcp \
    -X POST \
    -H 'accept: application/json, text/event-stream' \
    -d '{
  "jsonrpc": "2.0",
  "id": "0",
  "method": "ping"
}'

List tools

To see what tools a server has registered:

Code
 
curl https://my-gateway.zuplo.dev/mcp \
    -X POST \
    -H 'accept: application/json, text/event-stream' \
    -d '{
  "jsonrpc": "2.0",
  "id": "0",
  "method": "tools/list"
}'

List prompts

To see what prompts a server has available:

Code
 
curl https://my-gateway.zuplo.dev/mcp \
    -X POST \
    -H 'accept: application/json, text/event-stream' \
    -d '{
  "jsonrpc": "2.0",
  "id": "0",
  "method": "prompts/list"
}'

List resources

To see what resources a server has available:

Code
 
curl https://my-gateway.zuplo.dev/mcp \
    -X POST \
    -H 'accept: application/json, text/event-stream' \
    -d '{
  "jsonrpc": "2.0",
  "id": "0",
  "method": "resources/list"
}'

Call tool

To manually invoke a tool by name:

Code
 
curl https://my-gateway.zuplo.dev/mcp \
    -X POST \
    -H 'accept: application/json, text/event-stream' \
    -d '{
  "jsonrpc": "2.0",
  "id": "1",
  "method": "tools/call",
  "params": {
    "name": "my_tool",
    "arguments": {}
  }
}'

For more complex tools, you'll need to provide the schema compliant arguments. Note the inputSchema for the tool from tools/list to appropriately craft the arguments.

Get prompt

To execute a prompt with parameters:

Code
 
curl https://my-gateway.zuplo.dev/mcp \
    -X POST \
    -H 'accept: application/json, text/event-stream' \
    -d '{
  "jsonrpc": "2.0",
  "id": "1",
  "method": "prompts/get",
  "params": {
    "name": "my_prompt",
    "arguments": {
      "param1": "value1"
    }
  }
}'

For prompts with parameters, provide the required arguments object based on the prompt's schema from prompts/list.

Read resource

To read a resource by its URI:

Code
 
curl https://my-gateway.zuplo.dev/mcp \
    -X POST \
    -H 'accept: application/json, text/event-stream' \
    -d '{
  "jsonrpc": "2.0",
  "id": "1",
  "method": "resources/read",
  "params": {
    "uri": "mcp://resources/my_resource"
  }
}'

Use the URI from resources/list to specify which resource to read.

OAuth Testing

If you have configured OAuth authentication for your MCP Server, you can use the MCP Inspector to test the OAuth flow.

Hit the Open Auth Settings button in the Inspector UI to start the OAuth flow. When first setting up the OAuth flow, it's recommmended to use the Guided OAuth Flow which you will see when you open the OAuth settings. This will allow you to debug the flow step by step.

The OAuth flow involves the following steps, as shown in the MCP inspector guided auth flow. After you've checked each step, click the Continue button in the MCP Inspector UI to move to the next step.

1. Metadata Discovery: The MCP Inspector will make a request to the .well-known/oauth-protected-resource endpoint to learn about the OAuth configuration. The MCP Inspector will then make a request to the Authorization server which you configured in the OAuthProtectedResourcePlugin, which will return the metadata it needs to continue with the OAuth flow.

   If you see errors in this part, check that you have correctly added the OAuthProtectedResourcePlugin to your zuplo.runtime.ts file, and that you have correctly configured the authorizationServers value to be the canonical URL of your Authorization server, and registered an OAuth policy to the route of your MCP server.

2. Client Registration: The MCP Inspector will try to use Dynamic Client Registration to register a new client with the Authorization server. Note that not all MCP Clients require this, however at this time, the MCP Inspector does. You will need to enable Dynamic Client Registration on your Authorization server if you want to test the full flow through the MCP Inspector.

   If you see errors in this step, check that you have enabled Dynamic Client Registration on your Authorization server.

3. Preparing Authorization: The MCP Inspector will then redirect the user to the authorization server to login and authorize the MCP Client. Click the redirect link in the Authorization URL section to be prompted to login. After logging in, you will be given a code to copy in to the next step.

4. Request Authorization and acquire authorization code: Take the copied code from the last step and paste it in to the MCP Inspector and input it into the box.

5. Token Request: The MCP Inspector will do PKCE and make a request to the token endpoint of your Authorization server to exchange the authorization code for an access token. This is attached as the Authorization header when calling your MCP server, typically as a Bearer token.

6. Authentication Complete: You should now see a success message in the MCP Inspector. You can now hit the Connect button to connect to your MCP server.

If you see errors in the flow in steps 2-6, check that you have correctly configured your Authorization server to support the OAuth 2.0 Authorization Code Grant with PKCE and Refresh Tokens.

MCP Client

By connecting to an LLM enabled MCP Client, you can test the true end to end experience.

Many clients (like OpenAI, Claude Desktop, or Cursor) let you define the remote server URL and the name. For example, in Cursor, you can add your MCP server like so:

Code
 
{
  "mcpServers": {
    "my-custom-mcp-server": {
      "url": "https://my-gateway.zuplo.dev/mcp"
    }
  }
}