douglance PRD to Plan
Break a PRD into a phased implementation plan using vertical slices (tracer bullets). Output is a Markdown file in ./plans/.
Process
1. Confirm the PRD is in context
The PRD should already be in the conversation. If it isn't, ask the user to paste it or point you to the file.
2. Explore the codebase
If you have not already explored the codebase, do so to understand the current architecture, existing patterns, and integration layers.
3. Identify durable architectural decisions
Before slicing, identify high-level decisions that are unlikely to change throughout implementation:
- Route structures / URL patterns
- Database schema shape
- Key data models
- Authentication / authorization approach
- Third-party service boundaries
These go in the plan header so every phase can reference them.
4. Draft vertical slices
Break the PRD into tracer bullet phases. Each phase is a thin vertical slice that cuts through ALL integration layers end-to-end, NOT a horizontal slice of one layer.
When a phase has significant unknowns, include an explicit prototyping milestone to de-risk before full implementation. Prototypes are additive, testable, and clearly labeled. State criteria for promoting or discarding the prototype.
5. Quiz the user
Present the proposed breakdown as a numbered list. For each phase show:
- Title: short descriptive name
- User stories covered: which user stories from the PRD this addresses
Ask the user:
- Does the granularity feel right? (too coarse / too fine)
- Should any phases be merged or split further?
Iterate until the user approves the breakdown.
6. Write the plan file
Create ./plans/ if it doesn't exist. Write the plan as a Markdown file named after the feature (e.g. ./plans/user-onboarding.md). Use the template below.
Source PRD:
This plan is a living document. The Progress, Surprises & Discoveries, Decision Log, and Outcomes sections MUST be kept up to date as work proceeds. This plan must be fully self-contained — a novice with only this file should be able to implement the feature end-to-end.
Purpose / Big Picture
Explain in a few sentences what someone gains after this change and how they can see it working. State the user-visible behavior you will enable.
Architectural decisions
Durable decisions that apply across all phases:
- Routes: ...
- Schema: ...
- Key models: ...
- Interfaces & Dependencies: Name libraries, modules, types, traits/interfaces, function signatures that must exist. Be prescriptive.
- (add/remove sections as appropriate)
Context and Orientation
Describe the current state relevant to this task as if the reader knows nothing. Name key files and modules by full path. Define any non-obvious terms.
Phase 1:
User stories:
What to build
A concise description of this vertical slice. Describe the end-to-end behavior, not layer-by-layer implementation.
Validation and Acceptance
Phrase acceptance as observable behavior a human can verify — exact commands to run, expected output, what to observe. Not just "code compiles" but "running X produces Y". If tests are involved: "run <test command> — the new test <name> fails before the change and passes after."
Idempotence and Recovery
Can these steps be run multiple times safely? If a step is risky, provide retry/rollback path.
Phase 2:
User stories:
What to build
...
Validation and Acceptance
...
Progress
Use checkboxes with timestamps. Every stopping point must be documented, even if it requires splitting partial work into "done" vs "remaining."
- Phase 1: ...
- Phase 2: ...
Surprises & Discoveries
Document unexpected behaviors, bugs, performance tradeoffs, or insights discovered during implementation. Include concise evidence (test output is ideal).
- (none yet)
Decision Log
Record every decision made while working on the plan:
- (none yet)
Outcomes & Retrospective
Summarize outcomes, gaps, and lessons learned at major milestones or at completion. Compare result against original purpose.
- (to be filled at completion)