Requirements: Getting Aligned Before You Build

Before sketching architectures or debating React versus Vue, pause and define what you are actually building. This phase is about alignment—getting a shared understanding of the problem space, user needs, and business constraints.

Timebox this to roughly 10% of your interview. You are not writing a specification; you are proving you ask the right questions and think systematically about scope.

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Step 1: Functional Scope Definition

Break the feature set into two buckets: Core (without these, the product is broken) and Future (valuable but deferrable).

Sample: Social Content Platform

This separation helps you design for today's needs while keeping tomorrow's extensions feasible.

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Step 2: Non-Functional Requirements

These are the qualities that separate a working prototype from production-ready software.

Performance Budgets

• Time to Interactive: < 3 seconds on 3G
• Core Web Vitals: LCP < 2.5s, FID < 100ms, CLS < 0.1
• API Response: < 500ms for feed loads, < 200ms for interactions

Scale Expectations

• Concurrent Users: 50,000 peak
• Data Volume: 1M posts/day, 10M interactions/day
• Geographic Distribution: Global, with primary markets in US and EU

Compliance and Security

• Data Privacy: GDPR-compliant data handling
• Content Policy: Automated and human moderation workflows
• Authentication: OAuth 2.0, MFA support
• Accessibility: WCAG 2.1 AA compliance

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Step 3: Capacity Planning (Envelope Math)

Use rough estimates to reason about infrastructure needs. This demonstrates you think beyond code to operational realities.

Sample Calculation: Microblogging Platform

Assumptions:

• 2M Daily Active Users
• Each user creates 1.5 posts/day on average
• Each user views feed 8 times/day
• Peak traffic is 3x average

Write Load:

• Daily posts: 2M × 1.5 = 3M posts/day
• Average writes: 3M ÷ 86,400 ≈ 35 posts/second
• Peak writes: 35 × 3 = 105 posts/second

Read Load:

• Daily feed views: 2M × 8 = 16M requests/day
• Average reads: 16M ÷ 86,400 ≈ 185 requests/second
• Peak reads: 185 × 3 = 555 requests/second

This informs decisions about caching layers, database sharding, CDN requirements, and monitoring thresholds.

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Step 4: User Journey Mapping

Identify the key flows users will experience and their success criteria.

Primary Journeys

1. New User Onboarding

   • Sign up → profile setup → follow suggestions → first post
   • Success: User publishes content within 5 minutes

2. Content Discovery

   • Open app → browse feed → engage with posts → discover new accounts
   • Success: 60% of sessions include at least one engagement

3. Content Creation

   • Compose post → add media → publish → monitor engagement
   • Success: Post appears in followers' feeds within 30 seconds

4. Social Interaction

   • Comment on post → reply to comments → react to responses
   • Success: Real-time updates without page refresh

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Step 5: Technical Constraints and Context

Understand the environment your solution will operate within.

Platform Requirements

• Primary: Mobile web (70% of traffic)
• Secondary: Desktop web (25% of traffic)
• Future: Native iOS/Android apps (5% of traffic)

Integration Points

• Authentication: Existing OAuth provider (Auth0, Firebase)
• Media Storage: AWS S3 or similar object store
• Push Notifications: FCM for web, APNs for future native apps
• Analytics: Integration with existing data warehouse

Team and Timeline

• Development Team: 4 frontend engineers, 2 backend engineers
• Timeline: MVP in 12 weeks, full feature set in 20 weeks
• Existing Stack: Node.js backend, PostgreSQL, Redis

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Step 6: Data Entity Overview

Sketch the core information your system will manage—this anchors API design and state management decisions.

Primary Entities

User

• Profile information: username, display name, avatar, bio
• Social graph: followers, following counts
• Preferences: privacy settings, notification preferences

Post

• Content: text, media URLs, creation timestamp
• Metadata: author, engagement counts, visibility settings
• Relationships: comments, reposts, reactions

Engagement

• Actions: likes, comments, shares, bookmarks
• Actors: user performing action, target post/comment
• Temporal: timestamp, context (e.g., from which feed)

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Effective Requirements Questions

Scope Clarification

• "What's the minimum feature set for a successful launch?"
• "Who are the primary user personas, and how do their needs differ?"
• "Are there any features explicitly out of scope for this design?"

Constraints Discovery

• "What performance benchmarks must we hit?"
• "Are there regulatory requirements that constrain our data handling?"
• "Do we need to integrate with existing systems?"

Scale Assumptions

• "How many users do we expect in the first year?"
• "What's the anticipated growth rate?"
• "Are there seasonal or event-driven traffic spikes we should plan for?"

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With requirements clarified, you are ready to move into Architecture—where you will map these needs to technical components, data flows, and system boundaries.

Next: Architecture Design - Learn how to structure frontend applications that deliver on these requirements while remaining maintainable and extensible.