AI-Enabled Legacy Modernisation Playbook

What this artefact is

Individually deliverable feature specifications decomposed from the signed-off PRD. Each feature file is self-contained and describes a slice of the re-engineered system in enough detail for a delivery team to begin work.

How it’s produced

Feature specifications are produced by the prd-to-features skill, which reads the PRD, identifies natural feature boundaries, and generates one file per feature. The skill proposes a feature breakdown and waits for confirmation before writing any files.

What it contains

Each feature specification follows a structured template with up to 21 sections, included where the PRD provides sufficient material:

1. Metadata — feature ID, title, bounded context, priority, and effort estimate
2. Problem statement — what problem this feature solves and the benefit hypothesis
3. Target users — who uses this feature and what they need from it
4. Success criteria — measurable outcomes that confirm the feature works as intended
5. Scope — what is in and out of scope for this feature
6. User stories — Given/When/Then format with acceptance criteria
7. Wireframes — ASCII wireframes using Unicode box-drawing characters
8. UI/layout specifications — detailed enough for designers to mock up
9. Business rules — rules specific to this feature, traced back to the PRD
10. Data model — entities, attributes, and relationships relevant to this feature
11. Integration points — external systems or other features this depends on
12. Non-functional requirements — performance, availability, and scalability expectations
13. Legacy pain points — issues with the legacy implementation this feature should address
14. Dependencies — other features that must be delivered before or alongside this one
15. Assumptions — decisions made in the absence of confirmed information
16. Open questions — genuine ambiguities that need resolution before or during delivery
17. Definition of Done — checklist of conditions that must be met for the feature to be considered complete
18. Effort estimate — t-shirt size estimate with rationale
19. Glossary — domain terms specific to this feature

File naming

Feature files are named FT-XXX-feature-name.md, where XXX is a zero-padded sequential number. For example:

• FT-001-sample-registration.md
• FT-002-laboratory-assignment.md
• FT-003-results-entry.md

Quality criteria

• Every feature traces back to requirements in the PRD
• No fabricated requirements — gaps are captured in Open Questions
• User stories follow Given/When/Then format
• Features are independently deliverable where possible, with dependencies explicitly stated
• Domain language is consistent with the PRD’s ubiquitous language
• No placeholder text left in the final output

Example

The following snippets show key sections from a fictional sample search feature specification.

User story with acceptance criteria

US-001: Search by reference number

As a laboratory technician
I want to search for a sample by its reference number
So that I can quickly find a specific submission

Acceptance criteria:

  Given the user is on the Sample Search screen
  And the user has the "Viewer" role
  When the user enters "FS000192-07" in the Reference Number field
  And clicks Search
  Then the system displays matching submissions in the results list
  And the results show reference number, sender, date received, and status

Wireframe

┌─────────────────────────────────────────────┐
│ Sample Search                               │
├─────────────────────────────────────────────┤
│ Reference Number: [______________]          │
│ Sender:           [______________]          │
│ Date From:        [__________]              │
│ Date To:          [__________]              │
│                                             │
│ [Search]  [Clear]                           │
├─────────────────────────────────────────────┤
│ Ref        │ Sender    │ Received  │ Status │
│────────────┼───────────┼───────────┼────────│
│ FS000192-07│ Lab A     │ 15/01/2025│ Active │
│ FS000193-01│ Lab B     │ 16/01/2025│ Pending│
└─────────────────────────────────────────────┘

Business rules (excerpt)

Open questions (excerpt)