Writing Implementation Plans

Overview

Write comprehensive implementation plans assuming the implementer has zero context for the codebase and questionable taste. Document everything they need: which files to touch, complete code, testing commands, docs to check, how to verify. Give them bite-sized tasks. DRY. YAGNI. TDD. Frequent commits.

Assume the implementer is a skilled developer but knows almost nothing about the toolset or problem domain. Assume they don't know good test design very well.

Core principle: A good plan makes implementation obvious. If someone has to guess, the plan is incomplete.

When to Use

Always use before:

• Implementing multi-step features
• Breaking down complex requirements
• Delegating to subagents via subagent-driven-development

Don't skip when:

• Feature seems simple (assumptions cause bugs)
• You plan to implement it yourself (future you needs guidance)
• Working alone (documentation matters)

Bite-Sized Task Granularity

Each task = 2-5 minutes of focused work.

Every step is one action:

• "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

Too big:

### Task 1: Build authentication system
[50 lines of code across 5 files]

Right size:

### Task 1: Create User model with email field
[10 lines, 1 file]
Task 2: Add password hash field to User

[8 lines, 1 file]
Task 3: Create password hashing utility

[15 lines, 1 file]

Plan Document Structure

Header (Required)

Every plan MUST start with:

# [Feature Name] Implementation Plan
For Hermes: Use subagent-driven-development skill to implement this plan task-by-task.
Goal: [One sentence describing what this builds]
Architecture: [2-3 sentences about approach]
Tech Stack: [Key technologies/libraries]

Task Structure

Each task follows this format:

### Task N: [Descriptive Name]
Objective: What this task accomplishes (one sentence)
Files:
Create: exact/path/to/new_file.py
Modify: exact/path/to/existing.py:45-67 (line numbers if known)
Test: tests/path/to/test_file.py
Step 1: Write failing test

Step 2: Run test to verify failure
Run: pytest tests/path/test.py::test_specific_behavior -v
Expected: FAIL — "function not defined"
Step 3: Write minimal implementation

Step 4: Run test to verify pass
Run: pytest tests/path/test.py::test_specific_behavior -v
Expected: PASS
Step 5: Commit

Writing Process

Step 1: Understand Requirements

Read and understand:

• Feature requirements
• Design documents or user description
• Acceptance criteria
• Constraints

Step 2: Explore the Codebase

Use Hermes tools to understand the project:

# Understand project structure
search_files("*.py", target="files", path="src/")
Look at similar features

search_files("similar_pattern", path="src/", file_glob="*.py")
Check existing tests

search_files("*.py", target="files", path="tests/")
Read key files

read_file("src/app.py")

Step 3: Design Approach

Decide:

• Architecture pattern
• File organization
• Dependencies needed
• Testing strategy

Step 4: Write Tasks

Create tasks in order:

• Setup/infrastructure
• Core functionality (TDD for each)
• Edge cases
• Integration
• Cleanup/documentation

Step 5: Add Complete Details

For each task, include:

• Exact file paths (not "the config file" but src/config/settings.py)
• Complete code examples (not "add validation" but the actual code)
• Exact commands with expected output
• Verification steps that prove the task works

Step 6: Review the Plan

Check:

• [ ] Tasks are sequential and logical
• [ ] Each task is bite-sized (2-5 min)
• [ ] File paths are exact
• [ ] Code examples are complete (copy-pasteable)
• [ ] Commands are exact with expected output
• [ ] No missing context
• [ ] DRY, YAGNI, TDD principles applied

Step 7: Save the Plan

mkdir -p docs/plans
Save plan to docs/plans/YYYY-MM-DD-feature-name.md

git add docs/plans/
git commit -m "docs: add implementation plan for [feature]"

Principles

DRY (Don't Repeat Yourself)

Bad: Copy-paste validation in 3 places
Good: Extract validation function, use everywhere

YAGNI (You Aren't Gonna Need It)

Bad: Add "flexibility" for future requirements
Good: Implement only what's needed now

# Bad — YAGNI violation
class User:
    def __init__(self, name, email):
        self.name = name
        self.email = email
        self.preferences = {}  # Not needed yet!
        self.metadata = {}     # Not needed yet!
Good — YAGNI

class User:
    def __init__(self, name, email):
        self.name = name
        self.email = email

TDD (Test-Driven Development)

Every task that produces code should include the full TDD cycle:

• Write failing test
• Run to verify failure
• Write minimal code
• Run to verify pass

See test-driven-development skill for details.

Frequent Commits

Commit after every task:

git add [files]
git commit -m "type: description"

Common Mistakes

Vague Tasks

Bad: "Add authentication"
Good: "Create User model with email and password_hash fields"

Incomplete Code

Bad: "Step 1: Add validation function"
Good: "Step 1: Add validation function" followed by the complete function code

Missing Verification

Bad: "Step 3: Test it works"
Good: "Step 3: Run pytest tests/test_auth.py -v, expected: 3 passed"

Missing File Paths

Bad: "Create the model file"
Good: "Create: src/models/user.py"

Execution Handoff

After saving the plan, offer the execution approach:

"Plan complete and saved. Ready to execute using subagent-driven-development — I'll dispatch a fresh subagent per task with two-stage review (spec compliance then code quality). Shall I proceed?"

When executing, use the subagent-driven-development skill:

• Fresh delegate_task per task with full context
• Spec compliance review after each task
• Code quality review after spec passes
• Proceed only when both reviews approve

Remember

Bite-sized tasks (2-5 min each)
Exact file paths
Complete code (copy-pasteable)
Exact commands with expected output
Verification steps
DRY, YAGNI, TDD
Frequent commits

A good plan makes implementation obvious.