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Hello World Demo

Prerequisites

The instructions below rely on the following assumptions:

  1. This modulewise/demos repository has been cloned, and these instructions will be followed from within the hello-world directory.
  2. The Wasm Components have been built locally as described in components/README.md.
  3. The Modulewise Toolbelt has been installed locally as described in its README.

Run the Toolbelt MCP Server

In a separate terminal, start the Toolbelt with the Hello World tools:

toolbelt hello-world.toml

You can then use any MCP client or MCP-enabled Agent that supports the Streamable HTTP transport by connecting to http://localhost:3001/mcp.

Calling the Tools

A simple way to try out these tools is to use scripts in this repository that provde a barebones MCP client via curl commands.

Change into the scripts/mcp directory:

cd ../scripts/mcp

Initialize an MCP session:

./initialize.sh

If successful, you will see the protocol version and server info in a response.

With the session established, you can list available tools:

./list_tools.sh

You should see three tools:

  • hello.greeter.greet
  • aloha.greeter.greet
  • pirate.greeter.greet

First, call the hello.greeter.greet tool with a name parameter:

./call_tool.sh hello.greeter.greet name=World

You will see the greeting in the response:

{
  "jsonrpc": "2.0",
  "id": 3,
  "result": {
    "content": [
      {
        "type": "text",
        "text": "Hello World!"
      }
    ],
    "isError": false
  }
}

If you take a look at the hello-world.toml file passed to the toolbelt server above, you will see that the aloha variant uses the same greeter.wasm but includes config.greeting = "Aloha" to override the default "Hello" greeting:

./call_tool.sh aloha.greeter.greet name=World

And indeed, it responds with that greeting:

{
  "jsonrpc": "2.0",
  "id": 4,
  "result": {
    "content": [
      {
        "type": "text",
        "text": "Aloha World!"
      }
    ],
    "isError": false
  }
}

Finally, notice in hello-world.toml that the pirate variant is an interceptor. It adds a prefix and suffix, but otherwise composes with the aloha component.

[pirate]
uri = "../components/lib/intercepting-greeter.wasm"
config.prefix = "Ahoy and "
config.suffix = " Arrr!"
intercepts = ["aloha"]
exposed = true

Call it just like the others:

./call_tool.sh pirate.greeter.greet name=World

And see the result of the composed interception:

{
  "jsonrpc": "2.0",
  "id": 5,
  "result": {
    "content": [
      {
        "type": "text",
        "text": "Ahoy and Aloha World! Arrr!"
      }
    ],
    "isError": false
  }
}

If you want to explore the Wasm Components, have a look at the greeter project and its WebAssembly Interface Type (WIT) definition as well as the intercepting-greeter and its WIT.

License

Copyright (c) 2026 Modulewise Inc and the Modulewise Demos contributors.

Apache License v2.0: see LICENSE for details.