Detailed documentation that captures the requirements, behavior, and constraints of a product, giving teams a shared, authoritative description of what is to be built and how it should work. Stakeholders use them to align on scope, guide implementation, and verify that what ships matches what was intended.
Product Specifications
Product Specifications are the detailed documentation that describes what a product is supposed to be - its requirements, behavior, constraints, and the criteria by which it is judged done. Often captured as a product requirements document (PRD), they give everyone from engineering to stakeholders one authoritative account of scope and intent. A good specification is the reference point that keeps a build honest against what was actually agreed.
- Requirements - The functional and non-functional expectations the product must satisfy.
- Behavior - How the product should respond across the situations it will encounter.
- Constraints - The limits, dependencies, and rules the implementation has to respect.
- Acceptance criteria - Concrete, checkable conditions for what “done” means.
- Shared authority - A single artifact stakeholders align on rather than competing documents.
In API work I increasingly treat the machine-readable contract itself as the specification: an OpenAPI definition is the API’s product requirements, precise enough to design, mock, test, and govern against. When the spec is loose, drift creeps in between what was intended and what ships; when it is precise and version-controlled, it becomes the source of truth that documentation, Product Backlog Items, and governance all reference. That shift toward specifications as executable artifacts is exactly what makes an API legible to both teams and agents.
Referenced on the API Evangelist blog
Where this standard shows up across sixteen years of my writing at apievangelist.com — how it fits into API design, governance, and the agentic turn.
