How to Break Down a PRD for Claude Code Development: A Practical Guide

Mar 19, 2026

The Problem

I handed my PRD directly to Claude Code and expected it to implement everything. The PRD was detailed: user stories, acceptance criteria, technical constraints, and mockups. I thought I had done my homework. Claude started generating files, created components, wrote tests, and after two hours, I had a codebase that didn’t match my requirements.

The Reddit community confirmed what I experienced:

PRD → Claude starts coding immediately → Context overload
    → Ambiguous requirements interpreted wrong
    → Missing technical details invented
    → No clear ordering → Dependencies fail
    → Error cascade → Broken application

Experienced users on Reddit were blunt:

“Break the PRD into tiny vertical slices instead of letting it run on the whole thing at once.”

“PRDs are for humans, not AI. You need much more implementation level logic.”

The core issue: PRDs describe what users want, not how to build it. Claude needs the “how.”

Why PRDs Fail as Direct Input

PRDs are written for human stakeholders, not AI implementation. Here’s what goes wrong:

Context overload: A typical PRD has 20+ requirements. Claude tries to remember all of them while generating code. By requirement 15, it forgets requirement 3.

Ambiguity: PRDs use business language. “User should be able to manage their profile” doesn’t tell Claude what fields to include, how validation works, or what API endpoints to create.

Missing technical details: PRDs rarely specify database schema, API contracts, error handling strategies, or file organization. Claude invents these, often inconsistently.

No clear ordering: PRDs list features, not dependencies. Claude might build the UI before the API exists, or create a model without the migration.

Error cascade: One wrong interpretation early corrupts everything built on top of it. By the time you notice, 30 files need rewriting.

The Solution: Step-by-Step Breakdown

The workflow that works:

PRD → Step 1: Spec Document → Step 2: Vertical Slices → Step 3: Phase Implementation

Each step produces artifacts that Claude can execute.

Step 1: Create the Spec Document

Before any coding, transform the PRD into an implementation spec. This is what Reddit users meant by “generate a spec sheet first.”

The spec document answers technical questions the PRD leaves open:

# Project: [Name]

## Architecture Decisions
- Tech stack: [Frontend + Backend + Database]
- Key patterns: [e.g., Repository pattern, MVC, etc.]
- File organization: [Directory structure]

## Data Models
For each entity:
- Fields and types
- Relationships
- Validation rules

## API Endpoints
For each endpoint:
- Method and path
- Request body schema
- Response schema
- Error cases

## Component Structure
For each UI component:
- Props and state
- Behavior
- Styling approach

## Implementation Phases
Phase 1: Foundation (setup, models, base routes)
Phase 2: Feature A
Phase 3: Feature B
...

Here’s a concrete example of transforming a PRD section into a spec:

PRD excerpt:

Users should be able to:
- Register with email and password
- Log in and log out
- Update their profile information
- Reset their password via email

Spec transformation:

## Data Model: User
| Field | Type | Constraints |
|-------|------|-------------|
| id | UUID | Primary key, auto-generated |
| email | string | Unique, required, validated format |
| password_hash | string | Required, min 8 chars before hashing |
| created_at | timestamp | Auto-generated |
| updated_at | timestamp | Auto-updated |

## API Endpoints

### POST /auth/register
Request: { email: string, password: string }
Response: { success: boolean, user: { id, email } }
Errors:
  - 400: Invalid email format
  - 409: Email already exists

### POST /auth/login
Request: { email: string, password: string }
Response: { success: boolean, token: string }
Errors:
  - 401: Invalid credentials

### POST /auth/logout
Headers: Authorization: Bearer {token}
Response: { success: boolean }

### GET /users/me
Headers: Authorization: Bearer {token}
Response: { id, email, created_at }

### PATCH /users/me
Headers: Authorization: Bearer {token}
Request: { email?: string }
Response: { success: boolean, user: { id, email } }

## Phase Breakdown
Phase 1: User model + password hashing
Phase 2: Register endpoint
Phase 3: Login endpoint + JWT generation
Phase 4: Logout endpoint
Phase 5: Profile endpoints
Phase 6: Password reset

The spec removes ambiguity. Claude knows exactly what to build.

Step 2: Break Into Vertical Slices

Vertical slices cut through all layers. One slice = one complete, working piece of functionality.

The Reddit advice was clear: “tiny vertical slices.”

Wrong approach (horizontal):

All models → All routes → All tests → All UI
Result: Nothing works until everything is done

Right approach (vertical):

Slice 1: User model + register endpoint + test → WORKS
Slice 2: Login endpoint + session handling + test → WORKS
Slice 3: Logout endpoint + test → WORKS
Slice 4: Profile GET + test → WORKS
Slice 5: Profile PATCH + test → WORKS
Result: Each slice is deployable

Each slice has this structure:

┌─────────────────────────────────────────────────────────────┐
│                      Vertical Slice                         │
│                                                             │
│   ┌──────────┐   ┌──────────┐   ┌──────────┐              │
│   │  Model   │───│  Route   │───│   Test   │              │
│   └──────────┘   └──────────┘   └──────────┘              │
│                                                             │
│   Each slice is complete:                                   │
│   - Database operations work                                │
│   - API responds correctly                                  │
│   - Tests verify behavior                                   │
│   - Can be deployed independently                           │
│                                                             │
└─────────────────────────────────────────────────────────────┘

I create a slice document before implementation:

# Slice: User Registration

## What This Slice Delivers
Users can register with email and password.

## Files to Create
- models/user.py - User model with password hashing
- routes/auth.py - POST /auth/register endpoint
- tests/test_auth.py - Registration tests

## Dependencies
- Database connection (from foundation)
- Password hashing library (bcrypt)

## Implementation Steps
1. Create User model with email, password_hash fields
2. Add password hashing in model setter
3. Create /auth/register route
4. Add email validation
5. Add duplicate email check
6. Write tests:
   - Successful registration
   - Invalid email format
   - Duplicate email
   - Missing fields

## Success Criteria
- POST /auth/register creates user in database
- Password is hashed, not stored in plain text
- Duplicate emails return 409
- Invalid emails return 400
- All tests pass

Step 3: Implement in Phases

Phases build on each other. The Reddit workflow: “spec → plan → implementation” for larger tasks.

Phase 0: Setup (CLAUDE.md, project structure, dependencies)
Phase 1: Foundation (database, base models, utilities)
Phase 2: Core features (auth, main entities)
Phase 3: Secondary features (notifications, exports)
Phase 4: Polish (optimizations, edge cases)

Each phase has a prompt template:

Context: [Project description from spec]
Current state: [What's already complete]
This phase: [What to implement now]
Files to create/modify: [Specific list]
Constraints: [From CLAUDE.md]
Success criteria: [How to verify]

Example prompt for Phase 1:

Context: Building a user management system with authentication.
Spec document: [attached or referenced]

Current state:
- Project structure created
- Database connection configured
- CLAUDE.md exists with architecture constraints

This phase: Implement the foundation layer

Files to create:
1. models/base.py - Base model class
2. models/user.py - User model with fields from spec
3. utils/auth.py - Password hashing utilities
4. tests/test_base.py - Basic model tests

Constraints from CLAUDE.md:
- Use repository pattern for database access
- All models inherit from base class
- Maximum 400 lines per file
- No console.log statements

Success criteria:
- User model matches spec (fields, types, constraints)
- Password hashing works (verify with test)
- Base model provides common methods
- All tests pass

DO NOT implement any endpoints yet. This phase is models only.

Why This Matters

The structured approach delivers predictable outcomes:

Predictability: Each phase has clear inputs and outputs. I know what I’m getting before Claude starts.

Early validation: Problems surface in phase 1, not phase 4. Wrong interpretations get caught early.

Context management: Claude focuses on one slice at a time. No context dilution from unrelated features.

Debugging simplicity: When something breaks, I know exactly which slice has the problem. No hunting through 50 files.

WITHOUT BREAKDOWN:
  Claude runs for 2 hours → 40 files generated
  → 30% matches requirements → Start over

WITH BREAKDOWN:
  Spec: 30 minutes → Clear requirements
  Slice 1: 20 minutes → Working registration
  Slice 2: 15 minutes → Working login
  Slice 3: 10 minutes → Working logout
  Total: 75 minutes → Fully working auth system

Common Mistakes

Mistake	What Happens	Fix
Handing PRD directly	Context overload, inconsistent output	Transform to spec first
Skipping spec document	Claude invents technical details	Write spec with schemas and contracts
Horizontal slicing	Nothing works until everything is done	Cut vertical slices through all layers
Large slices	Context dilution within slice	Keep slices to 1-3 files
No verification between phases	Errors cascade to later phases	Test each phase before proceeding
Vague success criteria	Can’t tell when phase is done	Write specific, testable criteria
Forgetting dependencies	Phase 3 breaks Phase 1	Document dependencies in slice plan

PRD to Spec Conversion Example

Here’s a complete example of transforming a PRD into a spec:

Before (PRD format):

Feature: Blog Post Management

As a content creator, I want to create, edit, and publish blog posts so that
I can share my knowledge with readers.

Acceptance Criteria:
- Users can create new blog posts with title, content, and tags
- Users can edit existing blog posts
- Users can publish/unpublish blog posts
- Users can delete blog posts
- Blog posts display in reverse chronological order
- Tags can be added/removed from blog posts

Non-functional Requirements:
- Page load time under 2 seconds
- Mobile-responsive design

After (Spec format):

## Data Models

### Post
| Field | Type | Constraints |
|-------|------|-------------|
| id | UUID | Primary key |
| title | string | Required, max 200 chars |
| content | text | Required |
| status | enum | draft, published |
| author_id | UUID | Foreign key to User |
| published_at | timestamp | Nullable, set on publish |
| created_at | timestamp | Auto-generated |
| updated_at | timestamp | Auto-updated |

### Tag
| Field | Type | Constraints |
|-------|------|-------------|
| id | UUID | Primary key |
| name | string | Required, unique, max 50 chars |

### PostTag (Junction)
| Field | Type | Constraints |
|-------|------|-------------|
| post_id | UUID | Foreign key |
| tag_id | UUID | Foreign key |

## API Endpoints

### POST /posts
Request: { title: string, content: string, tag_ids?: string[] }
Response: { success: boolean, post: Post }

### GET /posts
Query: page?, limit?, status?
Response: { posts: Post[], total: number }

### GET /posts/:id
Response: { post: Post, tags: Tag[] }

### PATCH /posts/:id
Request: { title?, content?, tag_ids? }
Response: { success: boolean, post: Post }

### POST /posts/:id/publish
Response: { success: boolean, post: Post }

### DELETE /posts/:id
Response: { success: boolean }

## Phase Breakdown

Phase 1: Post model + CRUD endpoints
Phase 2: Tag model + tagging
Phase 3: Publishing workflow
Phase 4: Listing with pagination
Phase 5: UI components

## Slice Breakdown (Phase 1)

Slice 1.1: Post model + migration
Slice 1.2: POST /posts endpoint
Slice 1.3: GET /posts/:id endpoint
Slice 1.4: PATCH /posts/:id endpoint
Slice 1.5: DELETE /posts/:id endpoint

The spec leaves nothing to interpretation. Claude executes without guessing.

Summary

In this post, I showed how to transform PRDs into Claude Code-friendly format. The key insight: PRDs are for humans, not AI. Claude needs specs with implementation details, vertical slices with clear boundaries, and phases with verification gates.

The workflow that works:

Spec Document: Transform business requirements into technical specifications with schemas, contracts, and validation rules
Vertical Slices: Break features into complete, working pieces that span all layers
Phased Implementation: Build foundation first, then features incrementally with verification between phases

When I stopped handing PRDs directly and started creating specs with vertical slices, my success rate went from 30% to near 100%. Claude became a reliable implementation partner instead of an unpredictable code generator.

Final Words + More Resources

My intention with this article was to help others share my knowledge and experience. If you want to contact me, you can contact by email: Email me

Here are also the most important links from this article along with some further resources that will help you in this scope:

👨‍💻 Reddit: Breaking Down PRDs for Claude Code
👨‍💻 Anthropic Claude Code Documentation

Oh, and if you found these resources useful, don’t forget to support me by starring the repo on GitHub!