What are functional requirements?
Functional requirements describe the specific features, behaviors, and actions that a software system must perform.
They explain what the system should do from the user’s perspective and directly influence scope, estimation, and implementation.
Functional requirements turn high level business goals into concrete actions, workflows, and system outcomes.
Why functional requirements matter
- define exactly what needs to be built
- remove ambiguity during estimation and planning
- help designers and developers understand expected system behavior
- allow QA teams to create accurate test cases
- protect against scope creep by documenting what is included
- serve as the foundation for acceptance criteria and user stories
Without clear functional requirements, projects risk misunderstandings, rework, and missed expectations.
Examples of functional requirements
User management
- users can create accounts with email and password
- users can reset passwords via verification email
- admins can deactivate or reactivate user accounts
E-commerce
- users can add items to cart and complete checkout
- the system calculates tax and shipping cost dynamically
- admins can update product inventory
dashboards and reporting
- users can filter reports by date range
- system exports reports to CSV
- charts update in real time when filters change
workflows
- the system sends notifications when tasks are overdue
- managers approve or reject requests from employees
- files uploaded by users are stored and scanned for viruses
Functional requirements vs business requirements
| Aspect | Functional requirements | Business requirements |
|---|---|---|
| Focus | What the system must do | Why the project exists |
| Level | Detailed features | High level goals |
| Example | Allow users to upload documents | Reduce manual document processing |
| Used by | Dev team, QA, designers | Stakeholders, product owners |
Functional requirements support business requirements by defining the features needed to achieve the business goal.
Functional requirements vs non functional requirements
| Aspect | Functional | Non functional |
|---|---|---|
| Definition | Actions and behaviors | Quality attributes |
| Example | User can update profile | Page loads under 2 seconds |
| Focus | What system does | How well it performs |
Both are essential for accurate planning and estimation.
How to write clear functional requirements
1. Use simple, observable language
Describe user actions and system responses.
Example:
When the user clicks “Submit”, the system saves the form and shows a confirmation message.
2. Avoid technical implementation details
Focus on outcomes, not code or tools.
3. Keep requirements testable
Each requirement should be measurable by QA or acceptance testing.
4. Use consistent structure
Start requirements with verbs like: create, update, view, upload, filter, export.
5. Break down complex features
Split larger functionalities into smaller, manageable requirements.
6. Link to acceptance criteria
Functional requirements describe behavior.
Acceptance criteria define how to verify it.
Functional requirement document example
FUNCTIONAL REQUIREMENTS
Project: Recruiting Platform
Version: 1.0
1. User registration
• users can register with email and password
• system sends activation email
• users can log in after verification
2. Job listings
• users can search jobs by keyword and location
• users can save jobs to favorites
• admins can publish or unpublish job listings
3. Applications
• users can submit applications with CV and cover letter
• system sends notification to recruiter
• recruiter can update application status (new, in review, rejected)Common mistakes
- Vague requirements like “system should be user friendly”
- Mixing non functional attributes with features
- Not defining edge cases
- Specifying implementation instead of behavior
- Skipping review with the client
- Not versioning requirement documents
Best practices
- review requirements with both the client and team
- keep requirements atomic and easy to track
- document assumptions and constraints
- connect requirements to user stories and acceptance criteria
- update requirements after discovery or changes in scope
FAQ
What are functional requirements in software development?
They describe what the software must do, including features, actions, and behaviors.
Why are functional requirements important?
Because they define scope clearly, guide development, and allow accurate estimation.
How are functional requirements different from business requirements?
Business requirements explain goals. Functional requirements explain the actions needed to achieve those goals.
Who writes functional requirements?
Usually product owners, business analysts, or the project team during discovery.
Should functional requirements change during the project?
They can evolve, but changes should be controlled through a clear change request process.