A few days ago I shared AU Agent Utilities, a small open-source MCP server I built for deterministic Australian business...

A few days ago I shared AU Agent Utilities, a small open-source MCP server I built for deterministic Australian business-day calculations.Since then I've been thinking less about the tool itself and more about the reason it needs to exist.A good example is this: 24 December 2021 + 1 NSW business day = 29 December 2021At first glance, an AI agent could easily assume the answer is Monday 27 December.But in NSW:25 December 2021 was Christmas Day26 December was Boxing Dayboth fell on a weekendMonday 27 December became the Christmas Day substitute holidayTuesday 28 December became the Boxing Day substitute holidaySo the next business day was:Wednesday 29 December 2021That is exactly the kind of calculation I don't want an AI model guessing from memory. Reasoning vs deterministic toolsLLMs are useful when a task requires interpretation, reasoning or language.But some tasks have a correct answer based on a defined set of rules.Business-day calculations are one of them.If an agent is calculati...