Functional Specification Skill

Use this skill when the user wants a Functional Specification, product requirements document, or other outcome-focused spec that should remain valid even if the implementation changes.

Core principle

Write the destination, not the journey.

• Describe what must be true for users, operators, or external systems.
• Describe observable behavior, policies, constraints, and acceptance criteria.
• Avoid locking the document to architecture, code structure, vendors, or execution plans unless those details are part of the external contract.

The spec should still read as correct if the team later changes the tech stack, data model, service boundaries, UI framework, or rollout approach.

What a good Functional Specification contains