Preview by default

Custom Reports at Mailchimp was headed for ~6 months of engineering. Before that spend, the interaction model had to be right: can someone build a report, read it, and trust it before they hit save?

The call was preview by default. Keep the report up while the query changes. No “generate report” dead end. You see what you're building as you build it.

This is a tiny recreation of that pattern—fake local data, a handful of controls. The write-up is on Custom Reports.