Az Infra Harness is a small open source tool we built at Zure to help coding agents generate better Azure infrastructure code by guiding them through a structured planning conversation before they write any Bicep or Terraform. In this session we share what we learned building it: how it's structured, how it evolved as we used it ourselves, and what the tradeoffs are of building custom agent tooling versus relying on general-purpose prompting. We'll walk through a live demo, and if you've ever wondered whether it's worth wrapping your AI workflows in purpose-built tooling, hopefully this gives you something concrete to think about.