Writing a good brief before you hire a Next.js developer is the single thing that separates projects that land on time from ones that drift for months. After working through 15+ headless builds — some I briefed myself, many I was handed — the pattern is consistent: the brief determines the outcome more than the developer does.
The four mistakes I see in almost every agency brief
'Just like our current site, but faster.' This shows up verbatim more than you'd expect. It tells a developer nothing about what 'faster' means to you (sub-2-second load? better Google scores? reduced bounce?), and it implicitly asks them to replicate a structure that probably needs rethinking. Developers will fill the gaps with their own assumptions. Those assumptions will be wrong, and you'll pay to fix them.
Starting dev before the content model is agreed. A headless CMS like Sanity structures your content into types — a blog post is different from a case study, which is different from a team member profile. If your developer starts building while you are still deciding what content you have, one of two things happens: they build a generic schema that needs expensive rework, or they pause and wait while you figure it out. Neither is cheap. Content modelling is a design decision, not a dev task. It needs to happen before the first line of code.
