On this page
What is it?
The Feature Scope Document defines the functionality a product is expected to provide. It organizes functionality into modules and features and establishes what each feature is responsible for.
PRD
Product intent
FSD
Product functionality
BRD
Business rules
UFD
User behavior
Why do we need it?
A product idea is not detailed enough for implementation by itself. The FSD turns product-level goals into a concrete functional scope that other documents can work from.
Without FSD
With FSD
When do we create it?
The FSD is created after the product direction is sufficiently defined in the PRD and before detailed business rules, user flows, design specifications, and implementation are finalized.
This is an information-flow relationship, not a rigid waterfall.
Who benefits from it?
Product
Uses it to define the functional scope of the product.
Design
Uses it to understand what functionality needs to be represented in the experience.
Engineering
Uses it to understand the capabilities that need to be implemented.
AI agent
Uses it to understand which functionality exists and what each feature is responsible for.
What does it contain?
These are the proposed FSD sections for this methodology.
- 01
Product Modules
The major functional areas of the product.
- 02
Features
The individual capabilities within each module.
- 03
Feature Purpose
Why each feature exists from a functional perspective.
- 04
Feature Description
What the feature allows the user or system to do.
- 05
Feature Scope
What is included within the feature and what is outside its responsibility.
- 06
Priority
The importance or implementation priority of the feature.
- 07
MVP / Future Scope
Whether the feature belongs to the initial product scope or a later phase.
- 08
Dependencies
Other features or product capabilities that the feature relies on.
- 09
Feature States / Conditions
Only high-level functional states that are necessary to understand the feature.
What does a feature look like?
Feature
- Feature ID
- FEAT-001
- Feature name
- Create Project
- Module
- Projects
Purpose
Allow users to create a project to organize their work.
Description
Users can create a new project within the product.
Scope
Included
- Project creation
- Required project information
- Successful creation
Excluded
- Project permissions
- Project analytics
- Project deletion
- Priority
- High
- MVP
- Yes
- Dependencies
- User authentication
What does it NOT contain?
- Detailed business rules
- Detailed validation rules
- Complete user flows
- UI layouts
- Visual design
- Database schema
- API contracts
- Technical architecture
- Implementation code
FSD
Defines what the feature is responsible for.
BRD
Defines the rules the feature must follow.
UFD
Defines how the user moves through the feature.
DSD
Defines how the feature is experienced.
DDD / ASD / TAD
Define the engineering implementation.
How does AI use it?
The FSD gives the AI agent a functional map of the product. It tells the agent which capabilities exist, what each feature is responsible for, what belongs in the current scope, and which functionality is intentionally outside that scope.
AI understands
- Which modules exist
- Which features exist
- What each feature does
- What is in scope
- What is out of scope
- Which features are MVP
- Which dependencies exist
The FSD is not sufficient for implementation on its own — it defines what exists, not the rules, behavior, experience, or implementation behind it.
What
FSD
Rules
BRD
Behavior
UFD
Experience
DSD
Implementation structure
TAD
Agent behavior
AI Instructions
How does it connect to other documents?
The FSD provides the functional scope that later documents make more specific.
This isn't a strict waterfall — documents can inform each other and evolve together.
FSD
Create Project
BRD
What rules must Create Project follow?
UFD
How does the user create a project?
DSD
How should the experience behave and look?
DDD
What data does Create Project require?
ASD
How is Create Project communicated?
TAD
How is it structured in the application?
DR
When should it be implemented?
AI Instructions
How should the agent implement the task?
Example
Feature concept
Create a Project
FSD perspective
Users can create a project.
PRD
Why
Users need a way to organize their work into projects.
FSD
What
Users can create a project.
BRD
Rules
What conditions must be satisfied?
UFD
Behavior
How does the user complete the action?
DSD
Interface
How should the experience behave and look?
DDD
Data
What information must be stored?
ASD
Communication
How does the client communicate with the backend?
TAD
Structure
How is the capability structured in the codebase?
DR
Order
When should it be implemented?
AI Instructions
Implementation
How should the AI agent implement it?
FSD Template
fsd-template.md
# Feature Scope Document
## 01. Product Modules
### Module
Description:
---
## 02. Features
### Feature
Feature ID:
Feature Name:
Module:
Purpose:
Description:
Scope:
Included:
-
Excluded:
-
Priority:
MVP / Future:
Dependencies:
-
Functional States / Conditions:
-
---
Common mistakes
- Listing features without defining their responsibility.
- Turning the FSD into a collection of UI screens.
- Putting detailed business rules inside feature descriptions.
- Defining complete user journeys inside the FSD.
- Mixing implementation decisions into feature scope.
- Leaving MVP boundaries unclear.
- Creating features without identifying their module or dependencies.
- Letting AI invent functionality that was never included in the feature scope.