Specify before coding: the spec is the source of truth and the code its consequence. My way of building product as a system.
It's not a tool, it's a way of working: before writing code, I write what has to exist and why. The specification stops being documentation that ages and becomes the origin from which everything else flows.
The real benefit is that knowledge stops living only in my head. Anyone (or an AI) can read the spec and know what to build and where it fits. This very site is a case in point: the Context rules and the code is its consequence.
It has a cost: it demands discipline to keep the spec in sync, and a validator that stops code and documentation from contradicting each other. In exchange, you scale without becoming the bottleneck.