Asset Panda MCP Calculator Wrapper

This is a real MCP server that wraps your calculator Lambda function and makes it available to Claude Desktop via the Model Context Protocol.

What This Does

``
Claude Desktop (MCP Protocol)
↓
MCP Calculator Wrapper (this package)
↓ HTTP
Calculator Lambda (AWS Lambda Function URL)
↓
Calculator Operations (add, subtract, multiply, divide, power, sqrt)
`

Setup for Claude Desktop (Windows)

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Your Claude Desktop config at C:\Users\reymondko\AppData\Roaming\Claude\claude_desktop_config.json:

`json
{
"mcpServers": {
"assetpanda-calculator": {
"command": "npx",
"args": ["-y", "assetpanda-mcp-calculator@1.0.22"]
}
}
}
`

Steps:
1. Update your Claude Desktop config with the above
2. Restart Claude Desktop
3. Ask Claude: "What's 25 times 4?"

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For testing local changes before publishing:

`json
{
"mcpServers": {
"assetpanda-calculator": {
"command": "node",
"args": ["\\\\wsl.localhost\\Ubuntu\\home\\reymondko\\pioneer\\packages\\mcp-calculator-wrapper\\index.js"]
}
}
}
`

Steps:
1. Make changes to index.js
2. Update config to point to local file
3. Restart Claude Desktop

How It Works

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Claude Desktop talks to this wrapper using the MCP protocol over standard input/output.

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The wrapper registers six calculator tools:
- add: Add two numbers
- Parameters: a (first number), b (second number)
- Returns: Sum of a and b

- subtract: Subtract one number from another
- Parameters: a (number to subtract from), b (number to subtract)
- Returns: Difference of a minus b

- multiply: Multiply two numbers
- Parameters: a (first number), b (second number)
- Returns: Product of a and b

- divide: Divide one number by another
- Parameters: a (dividend), b (divisor)
- Returns: Quotient of a divided by b

- power: Raise a number to a power
- Parameters: base (base number), exponent (exponent)
- Returns: Base raised to the exponent

- sqrt: Calculate square root
- Parameters: a (number to calculate square root of)
- Returns: Square root of a

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When Claude calls a calculator tool, the wrapper:
1. Receives MCP request from Claude Desktop
2. Converts it to HTTP POST request
3. Calls your Lambda at https://fwigg2gvf2sbsinmddyrwga2tq0zdthi.lambda-url.us-east-1.on.aws/mcp
4. Converts Zod schemas from Lambda to JSON Schema (for Claude compatibility)
5. Returns results back to Claude via MCP protocol

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The wrapper automatically converts Zod schemas returned by the Lambda to proper JSON Schema format that Claude Desktop can understand. This happens in the tools/list handler:

`javascript
// Convert Zod schemas to JSON Schema for all calculator tools
if (result.result?.tools) {
result.result.tools = result.result.tools.map(tool => {
const schemas = {
'add': {
type: 'object',
properties: {
a: { type: 'number', description: 'First number' },
b: { type: 'number', description: 'Second number' }
},
required: ['a', 'b']
},
// ... other tools
};
return {
name: tool.name,
description: tool.description,
inputSchema: schemas[toolName] || defaultSchema
};
});
}
`

Files

- index.js - Main MCP server implementation with schema conversion
- package.json - NPM configuration
- mcp.log - Runtime logs (created automatically)

Development

`bash


Install dependencies (if any added)

npm install

Test locally

node index.js
`

This starts the MCP server. It communicates via stdio, so you'll need an MCP client (like Claude Desktop) to interact with it.

Testing Locally

Test the wrapper directly:

`bash
node /home/reymondko/pioneer/packages/mcp-calculator-wrapper/index.js
`

Then in another terminal, send MCP messages:

`bash


Initialize

echo '{"jsonrpc":"2.0","method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"test","version":"1.0.0"}},"id":1}' | node index.js

List tools

echo '{"jsonrpc":"2.0","method":"tools/list","id":1}' | node index.js

Call add tool

echo '{"jsonrpc":"2.0","method":"tools/call","params":{"name":"add","arguments":{"a":5,"b":3}},"id":1}' | node index.js
`

Publishing to NPM

`bash


Update version in package.json

npm version patch # or minor, or major

Publish (requires NPM account and login)

npm publish --access public
`

After publishing, anyone can use:
`bash
npx assetpanda-mcp-calculator@latest
`

Important: When updating the package, use specific version numbers in Claude Desktop config to avoid NPM cache issues:

`json
{
"mcpServers": {
"assetpanda-calculator": {
"command": "npx",
"args": ["-y", "assetpanda-mcp-calculator@1.0.22"]
}
}
}
`

Change @1.0.22 to @1.0.23 after publishing a new version to force cache refresh.

Environment Variables

- MCP_API_URL: Your Lambda function URL (default: https://fwigg2gvf2sbsinmddyrwga2tq0zdthi.lambda-url.us-east-1.on.aws)

You can override this in Claude Desktop config:

`json
{
"mcpServers": {
"assetpanda-calculator": {
"command": "npx",
"args": ["-y", "assetpanda-mcp-calculator@1.0.22"],
"env": {
"MCP_API_URL": "https://your-custom-lambda-url.amazonaws.com"
}
}
}
}
`

Usage Examples

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Just ask natural language questions:
- "What's 25 times 4?"
- "Calculate the square root of 144"
- "What's 2 to the power of 8?"
- "Divide 100 by 5"
- "Add 42 and 58"

Claude will automatically use the MCP calculator tools.

Troubleshooting

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If you see errors like Unrecognized key(s) in object: 'error' or ZodError in Claude Desktop logs:

Cause: The Lambda is returning Zod schemas instead of JSON Schema.

Fix: This wrapper automatically converts Zod schemas to JSON Schema. Make sure you're using version 1.0.22 or later:

`bash


Clear NPM cache

rm -rf /mnt/c/Users/reymondko/AppData/Local/npm-cache/_npx

Update Claude Desktop config to specific version

Change: "assetpanda-mcp-calculator@latest"

To: "assetpanda-mcp-calculator@1.0.22"

Restart Claude Desktop

`

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If Claude Desktop keeps using an old version after publishing updates:

Cause: npx caches packages based on the package spec hash.

Fix:
1. Use specific version numbers instead of @latest in config
2. Delete NPM cache: rm -rf /mnt/c/Users/reymondko/AppData/Local/npm-cache/_npx
3. Restart Claude Desktop

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If you installed the package globally and it's not working:

Cause: Global installations can interfere with npx.

Fix:
`bash


Uninstall global package

npm uninstall -g assetpanda-mcp-calculator

Clear cache

rm -rf /mnt/c/Users/reymondko/AppData/Local/npm-cache/_npx

Restart Claude Desktop

`

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Make sure Node.js is accessible from Windows:

`powershell


In PowerShell, verify Node.js is installed

node --version

Should output: v18.0.0 or higher

`

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Check that the Lambda URL is correct and accessible:

`bash
curl -X POST "https://fwigg2gvf2sbsinmddyrwga2tq0zdthi.lambda-url.us-east-1.on.aws/mcp" \
-H "Content-Type: application/json" \
-d '{"jsonrpc":"2.0","method":"tools/list","id":1}'
`

Should return a list of calculator tools.

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1. Check Claude Desktop logs: Help → View Logs
2. Look for mcp-server-assetpanda-calculator.log
3. Verify the config file path is correct
4. Make sure you restarted Claude Desktop after changing config
5. Check that the wrapper is starting: look for === MCP Server starting === in logs

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The wrapper creates a log file at:
`
/home/reymondko/pioneer/packages/mcp-calculator-wrapper/mcp.log
`

Check this file for detailed request/response logging:

`bash
tail -f /home/reymondko/pioneer/packages/mcp-calculator-wrapper/mcp.log
`

Look for:
- === MCP Server starting === - Server initialized
- >>> Making Lambda request - Calling Lambda
- <<< Lambda response - Got Lambda response
- ERROR - Any errors

Lambda Function URL

Your current Lambda function URL is:
`
https://fwigg2gvf2sbsinmddyrwga2tq0zdthi.lambda-url.us-east-1.on.aws/mcp
`

This Lambda implements the calculator operations and returns results to the wrapper.

Architecture

`
┌─────────────────────┐
│ Claude Desktop │
│ (User asks math) │
└──────────┬──────────┘
│ MCP Protocol (stdio)
│ {"jsonrpc":"2.0","method":"tools/call",...}
↓
┌─────────────────────┐
│ MCP Wrapper │
│ (this package) │
│ - Converts MCP │
│ - Schema transform │
│ - Logging │
└──────────┬──────────┘
│ HTTPS POST
│ {"jsonrpc":"2.0","method":"tools/call",...}
↓
┌─────────────────────┐
│ Lambda Function │
│ (Calculator) │
│ - add, subtract │
│ - multiply, divide │
│ - power, sqrt │
└─────────────────────┘
``

Version History

- 1.0.22 - Fixed schema conversion (Zod → JSON Schema)
- 1.0.7 - Initial release with basic calculator operations

Related Packages

- assetpanda-mcp-kb - Knowledge Base search MCP wrapper
- @assetpanda/mcp-client - Asset Panda MCP client wrapper

License

ISC