Write product requirements that can be built

A useful spec is short enough to read and specific enough to build. It names users, the job, the screens, and the definition of done.

The minimum spec

1. Primary user and the job they hire the product to do.
2. The happy path, step by step.
3. Data you must store.
4. What “done” looks like for the first release.
5. A list of explicit non-goals.

Keep it editable

Treat the spec as a working document. After each test, update the job, not just the feature list.