Onboarding custom sites with a single system prompt

I just replaced a whole onboarding flow with one system prompt.

For VellumUp (AI-powered SEO + GEO content automation), custom-coded sites were a pain. WordPress, Shopify, Webflow, Wix all had clear paths, but anything custom meant explaining manual setup, integrations, and blog structure in a way that never really clicked.

So I shipped a system prompt feature: users paste it into their AI and it auto-builds their blog page and site integration from there. No new UI, no wizard, just a prompt that knows how VellumUp works and how their site should hook into it.

What surprised me is how natural it felt to design onboarding as a conversation instead of a dashboard, and how much friction disappeared once I stopped forcing everyone through the same productized flow.

Has anyone else tried making onboarding “prompt-first” and letting the user’s own AI handle setup instead of building yet another UI for it?