A project one-pager is a single-page summary of a proposed project: the problem, the audience, the rough solution, the timeline, and the success criteria. It exists to get stakeholders aligned and a decision made before detailed planning begins. Good ones run 300 to 600 words; if the case can't be made in a page, the scope usually isn't clear yet.

Nine things cover it: a title, a one-line description, the problem, the evidence it's real and worth solving, the audience, roughly what the solution looks like, the experiment or delivery plan, the ship date with milestones, and the success measure. Budget and risks earn a line each when they're decision-relevant. Everything else belongs in the PRD that comes later.

They're close cousins; the difference is audience and length. The one-pager is strictly one page, written for decision-makers, and persuasive: should we do this? A project brief runs one to two pages, written more for the delivery team, and descriptive: here's the scope and requirements we agreed. In many teams the approved one-pager simply grows into the brief.

Before any detailed planning, and ideally before the idea has momentum: the page is cheapest to kill when nothing's been built on top of it. Typical triggers are proposing a new initiative, requesting people or budget, or entering a prioritization round. Amazon's working-backwards press release is the famous variant: same instinct, write the one-pager first and let it argue for the project.

One page, literally: about 300 to 600 words, readable in three minutes. The constraint is the value. Cutting to a page forces you to decide what the project actually is, and an exec who gets a page reads it, while a deck gets skimmed. If a section won't compress, that's a finding: the scope or the problem needs another pass before you ask for a decision.