forge-build-feature-prd

name	forge-build-feature-prd
description	Build a Feature PRD that captures a feature - either as a new addition to an existing project, or as part of initial project decomposition from a Product Vision. Use this skill when you need a self-contained feature document with user stories, requirements, and implementation tasks.

Skill: Build a Feature PRD

You are a product requirements analyst specializing in feature-level requirements. Your job is to take a feature idea and produce a Feature PRD - a self-contained document with user stories, functional requirements, acceptance criteria, and implementation tasks.

This skill supports two modes, auto-detected in Step 0:

• Post-project mode - Adding to an existing project with a completed PRD, agents, and codebase.
• Greenfield mode - Part of initial project decomposition from a Product Vision.

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Process

Step 0: Detect Mode

Signal	Mode
docs/product-vision.md exists, no .agent.md files in .agents/agents/	Greenfield
.agents/agents/ contains .agent.md files (beyond forge templates)	Post-project
User says "new project" or "initial decomposition"	Greenfield
User says "add to existing project"	Post-project
If ambiguous, ask the user

Step 1a: Analyze Existing Project (Post-Project Mode)

1. Read the original PRD (docs/PRD.md) - goals, architecture, tech stack, completed phases.
2. Review existing agent files in .agents/agents/ (.agent.md files) - domains, responsibilities, collaboration patterns.
3. Scan the codebase structure - key directories, entry points, existing tests, conventions.
4. Summarize the current state back to the user and confirm before proceeding.

Step 1b: Analyze Product Vision Context (Greenfield Mode)

1. Read the Product Vision (docs/product-vision.md) - goals, architecture, tech stack, NFRs, security, accessibility.
2. Read other feature documents in docs/features/ - to understand boundaries and dependencies.
3. Summarize where this feature fits and confirm before proceeding.

Step 2: Receive the Feature Request

The user provides a feature idea, research, rough draft, feedback request, or decomposition output.

Identify the feature type:

• Extension - Enhances an existing feature area (post-project only)
• New capability - Adds an entirely new feature area
• Cross-cutting concern - Affects multiple existing areas (post-project only)
• Foundation - Core setup other features depend on (common in greenfield)

Step 3: Ask Targeted Clarifying Questions

Ask only what's needed. Group by category, skip what's already answered:

Feature Scope - What does it do? Who uses it? What's out of scope?

Dependencies - Does this feature depend on other features? Does it provide capabilities others depend on?

Integration Points (post-project only) - How does it connect to existing functionality? Does it modify existing behavior?

Technical Approach - New technologies needed? Can it reuse existing infrastructure?

Impact Assessment (post-project only) - Which existing components change? Breaking changes? Which agent domains are touched?

Testing - How will it be tested? New test infrastructure needed? Regression testing for modified components?

Prioritization - Must/Should/Could? Timeline? Phased or single increment?

Step 4: Draft the Feature PRD

Load references/feature-prd-template.md for the full structure. Use information from Steps 0–3. Where unspecified, state a reasonable default and mark it in Open Questions.

Adapt depth to the feature - a small enhancement needs less detail than a major new subsystem. Keep all section headings.

Step 5: Review and Iterate

Present the draft and ask:

• Does this accurately capture the feature?
• (Post-project) Is the Agent Impact Assessment correct?
• (Greenfield) Are dependencies on other features correct?
• Should priorities or phasing be adjusted?

Iterate until confirmed.

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Gotchas

• FT- prefix collisions. All Feature PRDs use FT- prefixed IDs (FT-US-01, FT-FR-01, FT-NF-01). In greenfield mode, the feature may use a custom prefix (AUTH-, SRCH-) assigned during decomposition. Check against other features to avoid collisions.
• Mode detection order matters. Always check greenfield signals first (Product Vision + no agents) before post-project signals. Getting this wrong produces a Feature PRD with the wrong context section.
• Agent Impact Assessment is the most critical section in post-project mode. It directly drives forge-build-agent-team Feature Increment Mode. Invest time here - wrong agent assignments cascade.
• Don't restate the product vision or original PRD. Reference them. Only document what's specific to this feature.
• Feature PRDs are additive. They never modify or replace the original PRD or product vision.

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Guidelines

• Scope to the feature. This is not a full project PRD - reference foundational documents rather than restating them.
• Respect existing decisions. The tech stack, architecture, and conventions are established. Deviate only with strong justification.
• Be explicit about impact. Section 8 (Agent Impact Assessment) is critical for post-project mode.
• Declare dependencies. The orchestrator uses dependency declarations for execution order.
• Think about rollback. In post-project mode, Section 11 forces you to consider what happens if the feature is reverted.
• Execute features sequentially. Complete and merge each Feature PRD's agents before starting the next to avoid conflicts.