What you need before you start
A sentence is enough to begin. The useful version names the result, the timing that matters, who will approve the work, and anything you already have: files, examples, logins, brand notes or a budget range. A polished specification can wait.
The intake on post a project asks for the outcome, the must-have deliverables, timing, files, examples, a budget range and the approver. Missing answers become questions, not a reason to turn the brief away.