How to Write a Product Requirements Document (PRD)

CRITICAL: MUST save the final PRD to a file (e.g., documents/prd-<slug>.md). Do NOT only output in chat — always persist to disk.

When generating or refining a Product Requirements Document (PRD), follow these guidelines to ensure clarity, completeness, and alignment. This rule is designed to apply "Prompt Engineering" principles—clarity, constraints, and structure—to documentation.

0. Question Format (FR-UNIVERSAL.QA-FORMAT)

When asking the user a choice (audience, constraints, timeline):

• Each question MUST be a numbered list item (1., 2., …) — not a heading, bold-only line, or paragraph.
• For multi-select questions, when the user delegates with agent's choice (or equivalent), pick the subset yourself, emit a one-line justification of the pick, and proceed without re-asking for confirmation.

1. Core Principles

• Outcome-Oriented: Focus on the value delivered to the user, not just the technical implementation.
• Measurable: Requirements must be testable. Avoid vague terms like "fast" or "reliable" without metrics.
• Unambiguous: Remove ambiguity. If a requirement can be interpreted in multiple ways, it is a bug in the PRD.
• Living Document: Acknowledge that the PRD evolves. Mark unknowns clearly.

2. Writing Strategy (AI Instructions)

When asked to write a PRD:

1. Analyze the Request: Identify the core problem, target audience, and business goal.
2. Ask Clarifying Questions: If key context is missing (e.g., "Who is this for?", "What are the constraints?"), ask the user before generating the full doc. Follow the Question Format section above (FR-UNIVERSAL.QA-FORMAT).
3. Drafting: Use the template below.
4. Review: Check against the "Bad vs Good" examples in Section 4.
5. Persist: MUST write the final PRD to a file (e.g., documents/prd-<slug>.md or a path specified by the user). Do NOT only output the PRD in chat — always save it to disk using the file write tool (Write, write_to_file, etc.).

3. PRD Template

[PRD] {Title} {Status: Draft/Review/Approved}

1. Executive Summary

• Problem Statement: Clear, concise description of the user pain point or business opportunity.
• Proposed Solution: High-level overview of the feature/product.
• Value Proposition: Why is this important? What is the expected impact?

2. Success Metrics (KPIs)

• Primary Metric: The one number that defines success (e.g., Conversion Rate +5%).
• Guardrail Metrics: What specific negative outcomes must we avoid? (e.g., Latency < 200ms, Error rate < 1%).

3. Scope & User Stories

Target Audience: [Persona Name] - [Short Description]

Out of Scope:

• List specific features or use cases that are explicitly excluded to prevent scope creep.

4. Functional Requirements

• Core Logic: Detailed business rules (e.g., "If user is unverified, restrict access to X").
• Edge Cases: Empty states, error states, offline behavior.
• Data Requirements: Fields, validation rules, sources.

5. Non-Functional Requirements

• Performance: Latency, throughput, load expectations.
• Security: Authentication, authorization, data privacy (GDPR/PII).
• Compatibility: Browsers, devices, OS versions.

6. User Experience (UX)

• Flow: Describe the user journey (or insert Mermaid diagram).
• UI Elements: Key inputs, outputs, and feedback mechanisms.

7. Dependencies & Risks

• Dependencies: APIs, other teams, third-party services.
• Risks: Technical challenges, compliance issues, adoption risks.
• Mitigation: How will we handle these risks?

8. Open Questions

• List of unresolved questions that need input from stakeholders or technical research.

4. Examples: "Bad" vs "Good" Requirements

Ambiguity vs. Specificity

• 🔴 Bad: "The system should be fast."
• 🟢 Good: "API response time must be under 200ms for 95% of requests at a load of 100 QPS."

Implementation vs. Intent

• 🔴 Bad: "Add a blue button that says Save."
• 🟢 Good: "The user must be able to persist their changes. The action should be prominent and follow the primary action style guide."

Error Handling

• 🔴 Bad: "Handle errors gracefully."
• 🟢 Good: "If the backend is unreachable, display a toast notification with the message 'Connection failed, retrying...' and automatically retry 3 times with exponential backoff."

5. Visuals

Use Mermaid diagrams where possible to illustrate flows:

graph TD
    A[User Starts] --> B{Logged In?}
    B -- Yes --> C[Dashboard]
    B -- No --> D[Login Page]