Use when building a Crystallize side-by-side custom view — a web app embedded as an iframe next to the Crystallize item editor. Covers the URL parameter contract, the @crystallize/app-signal handshake, running local dev against Crystallize (with ngrok as an optional way to share the running app), CORS + Private Network Access, registering the custom view in Crystallize, and the minimal file layout for a Next.js shell. Do NOT use for generic Next.js setup, Crystallize API-only integrations without a UI, or non-iframe Crystallize extensions.
2026-04-22