Calculator MCP Server
Exposes add, subtract, multiply, and divide tools for performing arithmetic operations over stdio via the Model Context Protocol.
README
Calculator MCP Server
A small Model Context Protocol (MCP) server that exposes basic calculator operations over stdio.
Features
The server provides these tools:
| Tool | Description | Arguments |
|---|---|---|
add |
Adds two numbers | op1, op2 |
sub |
Subtracts the second number from the first | op1, op2 |
mul |
Multiplies two numbers | op1, op2 |
div |
Divides the first number by the second | op1, op2 |
All arguments must be numbers. div returns an error when op2 is 0.
Requirements
- Node.js 18 or later
- npm
Setup
Install the dependencies from this directory:
npm install
Run the server
Start the MCP server over stdio:
npm start
The server waits for an MCP client to connect, so it does not print normal application output to the terminal.
Test with the example client
The example client starts the server, lists its tools, and calls div with 10 and 0 to demonstrate the division-by-zero error:
npm run test-client
To test a successful operation, update the callTool arguments in mcp-client-test.ts, for example:
arguments: { op1: 10, op2: 2 },
Use MCP Inspector
Run the interactive MCP Inspector with:
npm run mcp-inspect
Open the URL printed by the command, then select a calculator tool and provide values for op1 and op2.
Project files
mcp-server.ts- MCP server and calculator tool definitionsmcp-client-test.ts- example MCP clientmcp-calculator.gif- tutorial walkthroughpackage.json- scripts and dependencies
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