add
Adds two numbers
LABSCO SUMMARY
The smallest thing to point a client at when you need to know whether the fault is yours or the server's.
Three tools, no credentials and no upstream service means anything that goes wrong is in your transport, your config or your client — nothing else is in the path to blame. Outside that diagnostic role it does nothing you would want: the answers are a greeting, a sum and a tool list.
What it is
A minimal reference server with three tools — echo, add and debug — whose only job is to answer, so a client's transport and tool-calling path can be exercised on its own.
What you get
- echo returns the message you sent with a Hello prefix, which is a completed round trip you can read
- add takes two numbers and returns the sum, exercising typed arguments rather than a string passthrough
- debug lists the tools and methods the server exposes, which is the shape your client should be rendering from a tool listing
Requirements
Nothing at all: no account, no key, and no service sitting behind it.
Setup effort
One command — npx mcp-hello-world
USE CASES
01
Proving a new client configuration actually reaches a server
Send a message and read the same message back with its prefix, then ask for the tool listing to confirm the client renders what a server advertises. Neither call can fail for a reason that is not the connection.
02
Checking that typed arguments survive the round trip
Send two numbers rather than a string and see the sum come back, which distinguishes a transport that works from a client that quietly stringifies everything it sends.
3 tools
Counted once with only startup setup. Other versions, modes or optional credentials may expose a different list.
debug
Lists all available tools and methods
echo
Echoes back a message with 'Hello' prefix
BEFORE YOU INSTALL
What to know first
Tools you get
3 tools when we connected.
Requires
npx on PATH
CONTEXT COST
Light Standing cost
Rated by the size of the 3 tool definitions that ride along on every turn, not by how many there are
INSTALLATION
Connect your client
Add the block to your client, or run the command directly.
Server setup
Configuration file
JSON
{
"mcpServers": {
"mcp-hello-world": {
"command": "npx",
"args": [
"mcp-hello-world"
]
}
}
}npx
TERMINAL
npx mcp-hello-world
