Writing Plans

Overview

Write comprehensive implementation plans assuming limited codebase context. Document everything needed: which files to touch for each task, code examples, testing approach, verification steps. Break work into bite-sized tasks following DRY, YAGNI, and TDD principles with frequent commits.

Assume the implementer is skilled but unfamiliar with the specific codebase and tooling.

When to Use

• Design is complete and ready for implementation
• Need to break down work into concrete tasks
• Preparing work for delegation or future execution
• Want clear verification steps for each task

Plan Location

Save plans to: docs/plans/YYYY-MM-DD-<feature-name>.md

Bite-Sized Task Granularity

Each step is one action (2-5 minutes):

• "Write the failing test" - step
• "Run it to make sure it fails" - step
• "Implement the minimal code to make the test pass" - step
• "Run the tests and make sure they pass" - step
• "Commit" - step

Break larger tasks into these atomic steps. Each step should be independently verifiable.

Plan Document Header

Every plan MUST start with this header:

# [Feature Name] Implementation Plan

**Goal:** [One sentence describing what this builds]

**Architecture:** [2-3 sentences about approach]

**Tech Stack:** [Key technologies/libraries]

---

Task Structure

### Task N: [Component Name]

**Files:**

- Create: `exact/path/to/file.py`
- Modify: `exact/path/to/existing.py:123-145`
- Test: `tests/exact/path/to/test.py`

**Step 1: Write the failing test**

```python
def test_specific_behavior():
    result = function(input)
    assert result == expected

Step 2: Run test to verify it fails

Run: pytest tests/path/test.py::test_name -v Expected: FAIL with "function not defined"

Step 3: Write minimal implementation

def function(input):
    return expected

Step 4: Run test to verify it passes

Run: pytest tests/path/test.py::test_name -v Expected: PASS

Step 5: Commit

git add tests/path/test.py src/path/file.py
git commit -m "feat: add specific feature"

Essential Elements

Exact File Paths

Always specify complete paths:

• Good: src/auth/validators.py
• Bad: "the validators file"

For modifications, include line ranges if known: config.json:45-52

Complete Code Examples

Include full, working code in the plan:

• Good: Show the complete function/test
• Bad: "Add validation for email field"

The implementer should be able to copy-paste code from the plan.

Exact Commands

Specify complete commands with expected output:

# Run specific test
pytest tests/auth/test_login.py::test_invalid_email -v

# Expected output
FAIL: AssertionError: Expected validation error

Verification Steps

Each task should explain how to verify it worked:

• What command to run
• What output to expect
• What to check manually if needed

Commit Guidelines

Encourage frequent, atomic commits:

• One logical change per commit
• Meaningful commit messages
• Follow conventional commits format:
  • feat: for new features
  • fix: for bug fixes
  • refactor: for code changes without behavior change
  • test: for test-only changes
  • docs: for documentation

Example Task

### Task 1: Email Validation

**Files:**

- Create: `src/validators/email.py`
- Test: `tests/validators/test_email.py`

**Step 1: Write the failing test**

```python
# tests/validators/test_email.py
from src.validators.email import validate_email

def test_rejects_invalid_email():
    result = validate_email("notanemail")
    assert result == {"valid": False, "error": "Invalid format"}

def test_accepts_valid_email():
    result = validate_email("user@example.com")
    assert result == {"valid": True}

Step 2: Run test to verify it fails

Run: pytest tests/validators/test_email.py -v Expected: FAIL with "ModuleNotFoundError: No module named 'src.validators.email'"

Step 3: Write minimal implementation

# src/validators/email.py
import re

def validate_email(email):
    pattern = r'^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$'
    if re.match(pattern, email):
        return {"valid": True}
    return {"valid": False, "error": "Invalid format"}

Step 4: Run test to verify it passes

Run: pytest tests/validators/test_email.py -v Expected: PASS (2 tests)

Step 5: Commit

git add tests/validators/test_email.py src/validators/email.py
git commit -m "feat: add email validation"

Best Practices

Be specific:

• Use exact file paths and line numbers
• Show complete code, not pseudocode
• Specify exact commands to run

Be minimal:

• Follow YAGNI - don't add features not in requirements
• Keep implementations simple
• Add complexity only when tests demand it

Be testable:

• Every feature has tests
• Tests written before implementation (TDD)
• Clear verification steps

Be incremental:

• Small commits after each working change
• Each task independently deliverable
• Build progressively

Common Mistakes to Avoid

• Don't write "add validation" - show the exact validation code
• Don't write "update config" - show exact config changes
• Don't skip test commands - always show how to verify
• Don't make tasks too large - break down into 2-5 minute steps
• Don't assume knowledge of project structure - specify full paths

Quick Reference

Final Rule

Plans should be executable by someone skilled but unfamiliar.
Every step: exact paths, complete code, clear verification.

Clear plans enable confident execution.