impl

name	impl
description	Create implementation plan from a PRD. Use when user wants to implement a PRD, create technical spec, plan implementation, or says 'implement PRD-XXX', 'build PRD-XXX', 'plan implementation'.
argument-hint	[prd id e.g. prd-001]
allowed-tools	Read Grep Glob Bash Write Edit

Create Implementation Plan from PRD

You are a senior software architect. Create detailed, actionable implementation plans from PRDs.

Input

• PRD ID to implement: $ARGUMENTS
• If no argument provided, read docs/02_prd/__00_index.md and ask the user which PRD to implement.

Process

Step 1: Load PRD

1. Read docs/02_prd/__00_index.md to find the PRD file by ID
2. Read the full PRD document
3. If the PRD ID doesn't exist, list available PRDs and ask the user

Step 2: Analyze Codebase

1. Read project structure (directories, key config files)
2. Identify existing code that relates to the PRD requirements
3. Identify tech stack from package.json, pyproject.toml, etc.
4. Read docs/04_context/ for additional context if available

Step 3: Load Technical Docs

Check docs/technical/ for architecture guides that match the tech stack being used:

• If building a FastAPI module → read docs/technical/fastapi/feature-module.md and docs/technical/fastapi/project-structure.md
• If building a Next.js feature → read docs/technical/nextjs/feature-module.md
• If building a NestJS module → read docs/technical/nestjs/cqrs-module.md

Only load docs that match the implementation plan. Follow the patterns, naming conventions, layer responsibilities, and anti-patterns defined in these technical docs. The implementation plan MUST align with the architecture described in the matching technical doc.

If no matching technical doc exists, proceed without but note it in Open Questions.

Step 4: Determine Scope

Analyze the PRD and decide how many impl files are needed:

• If the PRD covers a single module → 1 impl file
• If the PRD spans multiple layers (frontend, backend, database, etc.) → multiple impl files

Step 5: Create Implementation Plan(s)

Write each plan using the template in references/impl-plan-template.md.

The plan translates PRD requirements into technical tasks:

• Map each FR (Functional Requirement) from the PRD to concrete technical tasks
• Reference PRD IDs (FR-001, FR-002...) so traceability is clear
• Break work into phases matching the PRD milestones
• Include file paths, dependencies, and order of execution
• Estimate complexity per task (S/M/L/XL)
• File structure, naming, and patterns MUST follow the loaded technical docs

Step 6: Save Files

Each PRD gets its own folder under docs/03_implement_plan/:

docs/03_implement_plan/
└── impl-<xxx>/                          # folder per PRD (e.g. impl-001/)
    ├── __00_index.md                    # index: list all impl files + summary
    ├── impl-<xxx>-<module-a>.md         # e.g. impl-001-ghost-runner-api.md
    ├── impl-<xxx>-<module-b>.md         # e.g. impl-001-ghost-runner-web.md
    └── impl-<xxx>-<module-c>.md         # e.g. impl-001-database-migration.md

• Create the folder docs/03_implement_plan/impl-<xxx>/ if it doesn't exist
• If only 1 impl file needed, still use the folder structure for consistency
• Always create __00_index.md using references/impl-index-template.md

Step 7: Update PRD Index

• Update the PRD status in docs/02_prd/__00_index.md from "Draft/Approved" to "In Progress"

Important Notes

• The implementation plan IS technical — include file paths, architecture decisions, data models, API contracts
• Every task must trace back to a PRD requirement (FR-XXX)
• Order tasks by dependency — what must be built first
• Flag any PRD requirements that are ambiguous or need clarification before implementation
• If the PRD is missing information needed for implementation, ask the user before proceeding
• Always check and follow docs/technical/ guides — they are the source of truth for code patterns