What is Functional Specification?

Explained

Functional specs describe what the system must do: personas, journeys, business rules, and non-functional expectations at a product level. They feed PRDs, user stories, and agent guardrails so model behavior matches agreed intent before low-level technical specs.

Decision guides that use this term

• Legacy rewrite vs AI-assisted modernisation: should you start again or decode what you have?

Further reading

• Enterprise AI Transformation: A Strategic Roadmap for Competitive Advantage
• AI Design Platforms: The Four Pillars of Autonomous Product Innovation

Related terms

• Intent Goal or intention detected in a user's utterance (in conversational NLP).
• Guardrails Runtime constraints and policies that keep LLM outputs safe and on-brand.
• Acceptance Criteria Testable conditions that define when a feature or model output is “done” and correct.
• AI Bill of Materials Inventory of model lineage, datasets, dependencies, and licenses for an AI system.
• AI Governance Framework of policies, processes, and controls for responsible and ethical AI use in the enterprise.
• AI Native Architecture and processes designed from the ground up for AI, not as an afterthought.