Creating Feature Specifications
Introduction
Welcome back! In the previous lesson, you established your project-level constitution with CODEX.md, which defines the rules and standards that govern your entire project. Now we're going to zoom in one level deeper to feature-level specifications - the detailed blueprints that describe individual features within your project.
This lesson will teach you how to break down any feature into a complete specification that leaves no room for ambiguity. You'll learn what sections a specification needs, how to use AI to help generate them, and how to evaluate whether a specification is truly complete. A complete specification is especially critical when working with APIs, where clear communication between different parts of a system can make or break your project.
Key Elements Review
Before we dive into the details, let's refresh our understanding of what a specification actually is. A specification, often shortened to "spec," is a document that describes what a feature or component should do. Notice the emphasis on "what" rather than "how" - a good specification focuses on behavior and outcomes, not implementation details.
In the previous lesson, you encountered a simple specification for an API endpoint. Here's that example again:
This example is deliberately simple, containing just the bare minimum. Real-world features are more complex, which means their specifications need more depth and detail. The rest of this lesson will show you how to expand from this simple structure into complete, production-ready specifications.
We'll use a running example throughout this lesson: a user profile feature that includes an avatar, bio, and location. This is complex enough to demonstrate all the key concepts while remaining easy to understand.
The Purpose Section
Every specification begins with a purpose statement. This is your one-sentence explanation of what the feature does and why it exists. Think of it as the elevator pitch for your feature.
Here's the purpose statement for our user profile feature:
A good purpose statement is clear, concise, and gives immediate context to anyone reading the specification. It answers the fundamental question: "What is this feature for?" Anyone on your team should be able to read the purpose and immediately understand the feature's role in the larger system.
The purpose section serves as the anchor point for the rest of the specification. Every other section should support and elaborate on this central purpose. If you find yourself writing details that don't relate back to the stated purpose, you may need to either revise the purpose or reconsider whether those details belong in this specification.
