decomposing-prd-to-capabilities

Transform Product Requirements (PRD) into well-scoped Capability specs. Each capability represents what the product CAN DO—a large, cross-cutting vertical slice of functionality. **READ FIRST**: `/understanding-outcome-decomposition`

You must understand:

• Capability = what the product CAN DO (cross-cutting vertical slice)
• Capabilities may span many customer journeys
• The tree can start small (1 capability) and grow organically

<quick_start>

1. Read the PRD completely
2. Identify what the product should be CAPABLE of doing
3. Each capability is a cross-cutting area, not a customer journey
4. Create capability specs with BSP numbering based on dependencies
5. Start small—a single capability is valid

</quick_start>

Step 1: Analyze PRD for Product Abilities

Read the PRD and ask: "What should this product be CAPABLE of doing?"

Look for	Examples
Core functionality areas	"Generate documents", "Manage user identities"
Cross-cutting concerns	"Analytics", "Notifications", "Audit logging"
Infrastructure needs	"Test harness", "CLI tooling"
Integration points	"Third-party API integration", "Export/import"

Step 2: Identify Capability Boundaries

A capability is what the product CAN DO.

Examples of good capability names:

• "Document Generation"
• "Custody Account Management"
• "Monetization Platform"
• "Identity and Authentication Management"
• "SPI Peripheral Support" (for hardware library)

NOT capabilities:

• "User logs in and sees dashboard" (customer journey, not product ability)
• "Parse configuration file" (too small—story or feature level)
• "Sprint 1 work" (timeline, not functionality)

Step 3: Consider Starting Small

A single capability is valid. The tree grows organically.

spx/
├── product.prd.md
└── 21-core.capability/         ← Start with one
    └── 21-first-feature.feature/
        └── 21-first-story.story/

Later, you might add:

spx/
├── product.prd.md
├── 13-test-infrastructure.capability/  ← Discovered dependency
├── 21-core.capability/
└── 54-advanced.capability/             ← Added as product grows

Step 4: Determine BSP Ordering

Lower BSP = dependency. Order by what depends on what.

Pattern	BSP Strategy
Infrastructure (test harness, tooling)	Low BSP (10-20)
Core functionality	Mid BSP (21-50)
Advanced/optional features	High BSP (54-80)
Improvements/polish	Highest BSP (76-99)

BSP Calculation

Scenario	Formula	Example
First capability	21	21-core.capability/
Insert before 21	floor((10+21)/2) = 15	15-infra.capability/
Insert between 21 and 54	floor((21+54)/2) = 37	37-new.capability/
Append after 54	floor((54+99)/2) = 76	76-advanced.capability/

Parallel Capabilities (Same BSP)

Capabilities with the same BSP can be worked on in parallel:

37-users.capability/      ← Same BSP = parallel
37-billing.capability/    ← Same BSP = parallel
37-reports.capability/    ← Same BSP = parallel

Step 5: Write Capability Specs

For each capability, create:

spx/NN-{slug}.capability/
├── {slug}.capability.md
└── tests/                 # Created when starting implementation

Capability Spec Structure

Use the template from /managing-spx:

# Capability: {Name}

## Purpose

{What this product ability delivers and why it matters to users}

## Success Metric

- **Baseline**: {Current state}
- **Target**: {Expected improvement}
- **Measurement**: {How to track}

## Requirements

{Prose from PRD, focused on this capability's scope}

## Test Strategy

{Overview of how this capability will be tested—can span multiple levels}

## Outcomes

{Capability-level outcomes, if any—remember Principle 11}

## Architectural Constraints

{ADRs and PDRs that constrain this capability}

Note on Outcomes: A capability may have its own outcomes (high-level integration/E2E scenarios) OR it may have no direct outcomes—just features underneath. Both are valid.

Step 6: Validate Decomposition

For each capability:

□ Represents what the product CAN DO
□ Is a coherent cross-cutting area
□ Has clear boundaries with other capabilities
□ BSP reflects actual dependencies
□ Can be decomposed into ≤9 features (if needed now)

Example 1: SPI Library PRD → Capabilities

PRD excerpt:

"Hardware engineers need to configure SPI peripherals, generate Verilog, and verify on real FPGAs."

Analysis:

Product ability	Capability?
"SPI Peripheral Support"	YES - what the library CAN DO
"Code Generation"	YES - distinct ability
"FPGA Verification"	MAYBE - could be part of code gen or separate

Possible structures:

Option A: Start small

spx/
├── spi-library.prd.md
└── 21-spi-peripherals.capability/

Option B: Separate concerns

spx/
├── spi-library.prd.md
├── 13-test-infrastructure.capability/
├── 21-spi-peripherals.capability/
└── 54-fpga-verification.capability/

Both are valid. Start with A, grow to B as needed.

Example 2: Auth System PRD → Capabilities

PRD excerpt:

"Users need to register, log in, reset passwords, and manage their profiles. Support OAuth and magic links."

Analysis:

This is ONE capability: "Identity and Authentication Management"

spx/
├── auth-system.prd.md
└── 21-identity-auth.capability/
    ├── 21-registration.feature/
    ├── 37-login.feature/
    ├── 54-password-reset.feature/
    └── 76-oauth.feature/

NOT separate capabilities for login, registration, etc.—those are features.

Example 3: E-commerce Platform PRD → Capabilities

PRD excerpt:

"Customers browse products, add to cart, checkout with payment, track orders."

Analysis:

Product ability	Capability
Product catalog	21-catalog.capability/
Shopping cart	37-cart.capability/
Payment processing	37-payment.capability/
Order fulfillment	54-fulfillment.capability/

Note: cart and payment are parallel (same BSP)—neither depends on the other.

<anti_patterns>

What NOT to Create as Capabilities

Anti-pattern	Why wrong	Correct level
"User Login"	Too small	Feature
"Parse Config"	Too small	Story
"Sprint 1"	Timeline, not functionality	Not a container
"Customer Journey X"	Journey, not ability	May span capabilities
"API Endpoint /users"	Implementation detail	Story

Signals You're at Wrong Level

Signal	Problem
Capability name is a verb phrase	Might be a feature or story
Capability fits in 1-2 features	Might be too small
Capability name includes "and"	Might be multiple capabilities
Can't identify what product CAN DO	Needs clarification

</anti_patterns>

<success_criteria>

Decomposition complete when:

• Each capability represents what the product CAN DO
• Capabilities are cross-cutting vertical slices
• BSP ordering reflects dependencies
• Structure can grow organically (start small is OK)
• No capability is really a feature or story in disguise

</success_criteria>