Ask a language model to compute 2 + 3 * sqrt(16) and it will usually get it right. Ask it for 1,000,000 seconds in days, or a compound-interest figure over 30 years, and it will answer with total confidence — and sometimes be quietly wrong. It's predicting the next token, not running a calculator.
I already had a calculator. A whole site of them — 70-odd converters and calculators I'd built over the past year. So instead of writing another chatbot wrapper, I did the obvious thing: I let the AI call the real tools directly, over MCP.
Here's how that went, including the parts that didn't work.
MCP in one paragraph
The Model Context Protocol is a standard way for an AI assistant to discover and call external tools. The assistant asks your server "what can you do?", gets back a list of typed tools, and calls them with arguments — you run the actual code and hand back a real result. Claude speaks it, and a growing list of other clients do too. Think of it as giving the model hands instead of asking it to remember everything.
