Helps you document why you made design decisions by walking through a structured framework: what you decided, what context drove it, what alternatives you considered, what evidence you had, and what tradeoffs you accepted. It's meant for those moments when you're choosing between competing approaches or deviating from patterns, basically anywhere you'll need to justify your thinking later. The validation plan section is smart, it forces you to define upfront how you'll measure if you got it right. Worth using during design reviews or before handing off work. The real value is it keeps you honest about whether you're solving user problems or just following your own taste.
npx skills add https://github.com/owl-listener/designer-skills --skill design-rationale