What is a north star metric in product design?
A north star metric is the single most important metric a product team uses to measure whether the product is delivering value to its users. Spotify's north star metric is time spent listening. Airbnb's is nights booked. Slack's is messages sent. Each directly reflects users doing the core thing the product exists to help them do. When this metric goes up, users are getting more value; when it goes down, something has gone wrong.
Why is a north star metric important for UX?
A north star metric creates alignment between design, engineering, marketing, and business decisions by providing a single shared definition of what success looks like. Without a shared north star, different teams optimize for different outcomes: engineering for system performance, marketing for acquisition, design for satisfaction scores. When all teams share a north star metric that represents user value, every decision can be evaluated against whether it is expected to move that metric.
How does a north star metric differ from business metrics?
Business metrics like revenue measure outcomes for the company. A north star metric measures value delivered to users, which is the cause of which business outcomes are the effect. Spotify measures listening time rather than subscription revenue because listening time is what users value, and subscription revenue follows when users get enough value to pay. Optimizing directly for revenue can lead to decisions that extract short-term value from users at the cost of long-term trust and retention.