Plan

Plan Mode

Use this skill when the user wants a plan instead of execution.

Core behavior

For this turn, you are planning only.

• Do not implement code.
• Do not edit project files except the plan markdown file.
• Do not run mutating terminal commands, commit, push, or perform external actions.
• You may inspect the repo or other context with read-only commands/tools when needed.
• Your deliverable is a markdown plan saved under .poirot/plans/.

Output requirements

Write a markdown plan that is concrete and actionable.

Include, when relevant:

• Goal
• Current context / assumptions
• Proposed approach
• Step-by-step plan
• Files likely to change
• Tests / validation
• Risks, tradeoffs, and open questions

If the task is code-related, include exact file paths, likely test targets, and verification steps.

Save location

Save the plan with write_file under:

• .poirot/plans/YYYY-MM-DD_HHMMSS-<slug>.md

Treat that as relative to the active working directory / sandbox workspace. Poirot sandbox file tools are path-aware, so using this relative path keeps the plan with the workspace.

If no specific target path is provided by the runtime, create a sensible timestamped filename yourself under .poirot/plans/.

Interaction style

• If the request is clear enough, write the plan directly.
• If no explicit instruction accompanies the plan request, infer the task from the current conversation context.
• If it is genuinely underspecified, ask a brief clarifying question instead of guessing.
• After saving the plan, reply briefly with what you planned and the saved path.

Writing the Plan Well

The rest of this skill is the craft of authoring a good implementation plan — the content that goes inside the markdown file above.

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.

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

When a Full Implementation Plan Helps

Always use before:

• Implementing multi-step features
• Breaking down complex requirements
• Delegating work to a subagent (when available)

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

**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**

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

**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**

```python
def function(input):
    return expected
```

**Step 4: Run test to verify pass**

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

**Step 5: Commit**

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

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 Poirot tools to understand the project:

# Understand project structure
list_dir("src/")

# Look at similar features
bash("grep -rl 'similar_pattern' src/ --include='*.py'")

# Check existing tests
list_dir("tests/")

# Read key files
read_file("src/app.py")