Transform a feature request into a comprehensive implementation plan through systematic codebase analysis, external research, and strategic planning.

Core Principle: We do NOT write code in this phase. Our goal is to create a context-rich implementation plan that enables one-pass implementation success for AI agents.

Key Philosophy: Context is King. The plan must contain ALL information needed for implementation - patterns, mandatory reading, documentation, validation commands - so the execution agent succeeds on the first attempt.

Planning Process

Phase 1: Feature Understanding

Deep Feature Analysis:

Extract the core problem being solved
Identify user value and business impact
Determine feature type: New Capability/Enhancement/Refactor/Bug Fix
Assess complexity: Low/Medium/High
Map affected systems and components

Create User Story Format Or Refine If Story Was Provided By The User:

As a <type of user>
I want to <action/goal>
So that <benefit/value>

Phase 2: Codebase Intelligence Gathering

Use specialized agents and parallel analysis:

1. Project Structure Analysis

Detect primary language(s), frameworks, and runtime versions
Map directory structure and architectural patterns
Identify service/component boundaries and integration points
Locate configuration files (pyproject.toml, package.json, composer.json, etc.)
Find environment setup and build processes

2. Pattern Recognition (Use specialized subagents when beneficial)

Search for similar implementations in codebase
Identify coding conventions:
- Naming patterns (CamelCase, snake_case, kebab-case)
- File organization and module structure
- Error handling approaches
- Logging patterns and standards
Extract common patterns for the feature's domain
Document anti-patterns to avoid
Check CLAUDE.md for project-specific rules and conventions

3. Dependency Analysis

Catalog external libraries relevant to feature
Understand how libraries are integrated (check imports, configs)
Find relevant documentation in docs/, .claude/reference/ or other project docs
Note library versions and compatibility requirements

4. Testing Patterns

Identify test framework and structure (pytest, jest, PHPUnit, etc.)
Find similar test examples for reference
Understand test organization (unit vs integration)
Note coverage requirements and testing standards

5. Integration Points

Identify existing files that need updates
Determine new files that need creation and their locations
Map router/API registration patterns
Understand database/model patterns if applicable
Identify authentication/authorization patterns if relevant

Clarify Ambiguities:

If requirements are unclear at this point, ask the user to clarify before you continue
Get specific implementation preferences (libraries, approaches, patterns)
Resolve architectural decisions before proceeding

Phase 3: External Research & Documentation

Use specialized subagents when beneficial for external research:

Documentation Gathering:

Research latest library versions and best practices
Find official documentation with specific section anchors
Locate implementation examples and tutorials
Identify common gotchas and known issues
Check for breaking changes and migration guides

Technology Trends:

Research current best practices for the technology stack
Find relevant blog posts, guides, or case studies
Identify performance optimization patterns
Document security considerations

Compile Research References:

## Relevant Documentation

- [Library Official Docs](https://example.com/docs#section)
  - Specific feature implementation guide
  - Why: Needed for X functionality
- [Framework Guide](https://example.com/guide#integration)
  - Integration patterns section
  - Why: Shows how to connect components

Phase 4: Deep Strategic Thinking

Think Harder About:

How does this feature fit into the existing architecture?
What are the critical dependencies and order of operations?
What could go wrong? (Edge cases, race conditions, errors)
How will this be tested comprehensively?
What performance implications exist?
Are there security considerations?
How maintainable is this approach?

Design Decisions:

Choose between alternative approaches with clear rationale
Design for extensibility and future modifications
Plan for backward compatibility if needed
Consider scalability implications

Phase 5: Plan Structure Generation

Create comprehensive plan with the following structure:

What's below here is a template for you to fill for the implementation agent:

# Feature: <feature-name>

The following plan should be complete, but it's important that you validate documentation and codebase patterns and task sanity before you start implementing.

Pay special attention to naming of existing utils, types, and models. Import from the right files etc.

## Feature Description

<Detailed description of the feature, its purpose, and value to users>

## User Story

As a <type of user>
I want to <action/goal>
So that <benefit/value>

## Problem Statement

<Clearly define the specific problem or opportunity this feature addresses>

## Solution Statement

<Describe the proposed solution approach and how it solves the problem>

## Feature Metadata

**Feature Type**: [New Capability/Enhancement/Refactor/Bug Fix]
**Estimated Complexity**: [Low/Medium/High]
**Primary Systems Affected**: [List of main components/services]
**Dependencies**: [External libraries or services required]

---

## CONTEXT REFERENCES

### Relevant Codebase Files - IMPORTANT: YOU MUST READ THESE FILES BEFORE IMPLEMENTING!

<List files with line numbers and relevance>

- `path/to/file.py` (lines 15-45) - Why: Contains pattern for X that we'll mirror
- `path/to/model.py` (lines 100-120) - Why: Database model structure to follow
- `path/to/test.py` - Why: Test pattern example

### New Files to Create

- `path/to/new_service.py` - Service implementation for X functionality
- `path/to/new_model.py` - Data model for Y resource
- `tests/path/to/test_new_service.py` - Unit tests for new service

### Relevant Documentation - YOU SHOULD READ THESE BEFORE IMPLEMENTING!

- [Documentation Link 1](https://example.com/doc1#section)
  - Specific section: Authentication setup
  - Why: Required for implementing secure endpoints
- [Documentation Link 2](https://example.com/doc2#integration)
  - Specific section: Database integration
  - Why: Shows proper async database patterns

### Patterns to Follow

<Specific patterns extracted from codebase - include actual code examples from the project>

**Naming Conventions:** (for example)

**Error Handling:** (for example)

**Logging Pattern:** (for example)

**Other Relevant Patterns:** (for example)

---

## IMPLEMENTATION PLAN

### Phase 1: Foundation

<Describe foundational work needed before main implementation>

**Tasks:**

- Set up base structures (schemas, types, interfaces)
- Configure necessary dependencies
- Create foundational utilities or helpers

### Phase 2: Core Implementation

<Describe the main implementation work>

**Tasks:**

- Implement core business logic
- Create service layer components
- Add API endpoints or interfaces
- Implement data models

### Phase 3: Integration

<Describe how feature integrates with existing functionality>

**Tasks:**

- Connect to existing routers/handlers
- Register new components
- Update configuration files
- Add middleware or interceptors if needed

### Phase 4: Testing & Validation

<Describe testing approach>

**Tasks:**

- Implement unit tests for each component
- Create integration tests for feature workflow
- Add edge case tests
- Validate against acceptance criteria

---

## STEP-BY-STEP TASKS

IMPORTANT: Execute every task in order, top to bottom. Each task is atomic and independently testable.

### Task Format Guidelines

Use information-dense keywords for clarity:

- **CREATE**: New files or components
- **UPDATE**: Modify existing files
- **ADD**: Insert new functionality into existing code
- **REMOVE**: Delete deprecated code
- **REFACTOR**: Restructure without changing behavior
- **MIRROR**: Copy pattern from elsewhere in codebase

### {ACTION} {target_file}

- **IMPLEMENT**: {Specific implementation detail}
- **PATTERN**: {Reference to existing pattern - file:line}
- **IMPORTS**: {Required imports and dependencies}
- **GOTCHA**: {Known issues or constraints to avoid}
- **VALIDATE**: `{executable validation command}`

<Continue with all tasks in dependency order...>

---

## TESTING STRATEGY

<Define testing approach based on project's test framework and patterns discovered during research>

### Unit Tests

<Scope and requirements based on project standards>

Design unit tests with fixtures and assertions following existing testing approaches

### Integration Tests

<Scope and requirements based on project standards>

### Edge Cases

<List specific edge cases that must be tested for this feature>

---

## VALIDATION COMMANDS

<Define validation commands based on project's tools discovered in Phase 2>

Execute every command to ensure zero regressions and 100% feature correctness.

### Level 1: Syntax & Style

<Project-specific linting and formatting commands>

### Level 2: Unit Tests

<Project-specific unit test commands>

### Level 3: Integration Tests

<Project-specific integration test commands>

### Level 4: Manual Validation

<Feature-specific manual testing steps - API calls, UI testing, etc.>

### Level 5: Additional Validation (Optional)

<MCP servers or additional CLI tools if available>

---

## ACCEPTANCE CRITERIA

<List specific, measurable criteria that must be met for completion>

- [ ] Feature implements all specified functionality
- [ ] All validation commands pass with zero errors
- [ ] Unit test coverage meets requirements (80%+)
- [ ] Integration tests verify end-to-end workflows
- [ ] Code follows project conventions and patterns
- [ ] No regressions in existing functionality
- [ ] Documentation is updated (if applicable)
- [ ] Performance meets requirements (if applicable)
- [ ] Security considerations addressed (if applicable)

---

## COMPLETION CHECKLIST

- [ ] All tasks completed in order
- [ ] Each task validation passed immediately
- [ ] All validation commands executed successfully
- [ ] Full test suite passes (unit + integration)
- [ ] No linting or type checking errors
- [ ] Manual testing confirms feature works
- [ ] Acceptance criteria all met
- [ ] Code reviewed for quality and maintainability

---

## NOTES

<Additional context, design decisions, trade-offs>

Output Format

Filename: .claude/plans/{kebab-case-descriptive-name}.md

Replace {kebab-case-descriptive-name} with short, descriptive feature name
Examples: add-user-authentication.md, implement-search-api.md, refactor-database-layer.md

Directory: Create .claude/plans/ if it doesn't exist Archive: After implementation, move completed plans to .claude/plans/archive/

Quality Criteria

Context Completeness

All necessary patterns identified and documented
External library usage documented with links
Integration points clearly mapped
Gotchas and anti-patterns captured
Every task has executable validation command

Implementation Ready

Another developer could execute without additional context
Tasks ordered by dependency (can execute top-to-bottom)
Each task is atomic and independently testable
Pattern references include specific file:line numbers

Pattern Consistency

Tasks follow existing codebase conventions
New patterns justified with clear rationale
No reinvention of existing patterns or utils
Testing approach matches project standards

Information Density

No generic references (all specific and actionable)
URLs include section anchors when applicable
Task descriptions use codebase keywords
Validation commands are non-interactive and executable

Success Metrics

One-Pass Implementation: Execution agent can complete feature without additional research or clarification

Validation Complete: Every task has at least one working validation command

Context Rich: The Plan passes "No Prior Knowledge Test" - someone unfamiliar with codebase can implement using only Plan content

Confidence Score: #/10 that execution will succeed on first attempt

Report

After creating the Plan, provide:

Summary of feature and approach
Full path to created Plan file
Complexity assessment
Key implementation risks or considerations
Estimated confidence score for one-pass success