EARS Format Expert

Easy Approach to Requirements Syntax

Purpose: Write clear, testable requirements
Format: 5 requirement types

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Overview

EARS provides templates for writing unambiguous requirements.

5 Requirement Types

1. Ubiquitous: Always true
2. Event-Driven: Triggered by events
3. State-Driven: Depends on system state
4. Optional: May occur
5. Complex: Multiple conditions

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Templates

1. Ubiquitous Requirements

When: No conditions, always true.
Template: The [system] shall [action].

Examples:

• The system shall encrypt passwords using bcrypt.
• The API shall return JSON responses.

2. Event-Driven Requirements

When: Triggered by specific events.
Template: When [trigger], the [system] shall [action].

Examples:

• When user clicks "Submit", the form shall validate all fields.
• When payment succeeds, the system shall send confirmation email.

3. State-Driven Requirements

When: Depends on system state.
Template: While [state], the [system] shall [action].

Examples:

• While user is authenticated, the dashboard shall display personalized content.
• While battery is below 20%, the app shall enable power-saving mode.

4. Optional Requirements

When: Feature may or may not be used.
Template: Where [condition], the [system] shall [action].

Examples:

• Where dark mode is enabled, the UI shall use dark theme colors.
• Where GPS is available, the app shall show user location.

5. Complex Requirements

When: Multiple conditions or alternatives.
Template: If [condition], then [action], else [alternative].

Examples:

• If login succeeds, then redirect to dashboard, else display error message.
• If file size > 10MB, then compress before upload, else upload directly.

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Acceptance Criteria

Each requirement should include measurable acceptance criteria:

Example:

Requirement: When user submits login form, the system shall validate credentials.

Acceptance Criteria:
✓ Email format verified (RFC 5322)
✓ Password length ≥8 characters
✓ Validation completes in <100ms
✓ Error messages are user-friendly

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Anti-Patterns

❌ Avoid Ambiguity

Bad: The system should work fast.
Good: The system shall respond to API requests in <500ms (p95).

❌ Avoid Mixing Concerns

Bad: When user logs in, the system shall validate credentials and send welcome email.
Good: Split into two requirements (login validation + email notification).

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Validation Checklist

• Template: Correct EARS template used?
• Testable: Can be verified with tests?
• Unambiguous: No vague terms (e.g., "fast", "user-friendly")?
• Measurable: Quantifiable criteria provided?

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Related Skills

• moai-foundation-specs: SPEC writing
• moai-foundation-tags: Traceability

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Last Updated: 2025-11-20