Build a bounded calculator tool

Goal

Let an agent request arithmetic while keeping expression parsing and execution in a deterministic local function.

Steps

1. Define a calculator tool schema with explicit numeric operands and supported operators rather than accepting arbitrary code. [source03]
2. Dispatch tool_use blocks from client.messages.create to a parser that rejects names, imports, attributes, and oversized expressions. [source03]
3. Return a numeric result or a structured error as tool_result; test divide-by-zero and malicious input without evaluating Python eval. [source03]

How to verify

Check that supported arithmetic returns the expected number, division by zero returns a structured error, and inputs containing imports, attributes, or names never reach Python eval.

Troubleshooting

If an unsupported expression is accepted, narrow the parser to the explicit operator allowlist and add a regression case; never fall back to eval.