Especially the design principles are a collection of best practices. Part of it feels like reading Apple’s HIG or Material Design Guidelines. Part of it Refactoring UI. It’s what you learn (or wish you would learn) in design school. Or from a good mentor. Or acquire through years of experience and reading.
Curious: How certain are you that this is indeed the original system prompt, without further hallucination?
I'm pretty confident in it: I saw the same result from a few different attempts, it's consistent with how the app itself appears to work, and the GitHub Next Twitter account tweeted my article without noting any inaccuracies.
Generally my past experience has been that leaked system prompts aren't hallucinated. Models are very good at repeating text that's just been fed into them.
Hi! Kelsey here (PM from Spark team). I can confirm the system prompt shared in Simon's post wasn't hallucinated. We worked hard to instill good design principles into the prompt. We put it through its paces with a number of designers that are some of the best in the industry. I also went to Parsons School for Design and can confirm this is 100% something they teach you at a good design school! ^-^