Explore Code

Deep exploration of unfamiliar codebases to understand usage patterns before extraction or integration.

Overview

This skill helps users understand code they don't know, specifically when preparing to extract functionality into reusable libraries or components.

MANDATORY: User must specify what usage type to explore (e.g., "database reading patterns", "authentication flow", "API client usage").

The exploration answers three questions:

1. What is used - Which tables, APIs, components, functions
2. How it is used - Patterns, conditions, parameters, transformations
3. Where to use it - Call sites, contexts, triggering conditions

Key assumption: The project is unknown to the user. They're learning to extract, not verifying known behavior.

Output: A structured markdown file at planning/exploration-<topic>.md with precise usage inventory for extraction planning.

Process Flowchart

┌─────────────────────────────────────────────────────────────────┐
│                     User asks exploration question              │
└─────────────────────────────────────────────────────────────────┘
                                │
                                ▼
                    ┌───────────────────────┐
                    │  Ask scoping questions │◄────┐
                    └───────────────────────┘     │
                                │                 │
                                ▼                 │
                    ┌───────────────────────┐     │
                    │     Scope clear?      │─────┘
                    └───────────────────────┘ no
                                │ yes
                                ▼
                    ┌───────────────────────┐
                    │ Initial exploration   │
                    └───────────────────────┘
                                │
                                ▼
                    ┌───────────────────────┐
                    │ CHECKPOINT 1: Report  │
                    │ Ask: Focus areas?     │
                    └───────────────────────┘
                                │
                                ▼
                    ┌───────────────────────┐
                    │ Deep dive on areas    │◄────┐
                    └───────────────────────┘     │
                                │                 │
                                ▼                 │
                    ┌───────────────────────┐     │
                    │ CHECKPOINT 2: Report  │     │
                    │ Ask: Skip/add areas?  │     │
                    └───────────────────────┘     │
                                │                 │
                                ▼                 │
                    ┌───────────────────────┐     │
                    │   More areas?         │─────┘
                    └───────────────────────┘ yes
                                │ no
                                ▼
                    ┌───────────────────────┐
                    │ Synthesize findings   │
                    └───────────────────────┘
                                │
                                ▼
                    ┌───────────────────────┐
                    │ CHECKPOINT 3: Draft   │
                    │ Ask: Adjust format?   │
                    └───────────────────────┘
                                │
                                ▼
                    ┌───────────────────────┐
                    │ Generate final doc    │
                    └───────────────────────┘
                                │
                                ▼
                    ┌───────────────────────┐
                    │    Deliver document   │
                    └───────────────────────┘

Phase 1: Scoping Questions

MANDATORY: Ask these BEFORE any exploration.

Use the AskUserQuestion tool to understand:

1. Usage type (REQUIRED): "What specific usage do you want to explore?"
   • Examples: "database reading layer", "REST API client", "authentication flow", "file I/O patterns"
   • This MUST be specified - do not proceed without it
2. Extraction goal: "What are you planning to extract or create?"
   • Options: Standalone library, Internal module, API wrapper, Understanding only (no extraction)
3. Scope boundaries: "Which parts of the codebase are relevant?"
   • Options: Specific directories, Specific file types, Everything, Not sure (I'll explore)
4. Depth: "How detailed should the inventory be?"
   • Options: High-level patterns only, Detailed with all call sites, Exhaustive with parameters/conditions

Phase 2: Initial Exploration

After scoping, perform initial pass:

1. Find relevant files using Glob patterns based on scope
2. Identify key entry points - main files, exports, public APIs
3. Map top-level structure - directories, modules, packages

CHECKPOINT 1: Present initial findings to user

## Initial Scan Results

**Files found:** N files matching criteria
**Key entry points:** [list]
**Main directories:** [list]

**Potential focus areas:**
1. [Area A] - appears to handle X
2. [Area B] - appears to handle Y
3. [Area C] - appears to handle Z

**Which areas should I focus on?** (can select multiple or suggest others)

Wait for user response before continuing.

Phase 3: Deep Exploration

For each selected area, answer the three core questions:

3.1 What Is Used

Inventory everything the code interacts with for the specified usage type:

• Classes, structs, functions accessed
• External libraries or APIs called
• Resources (files, connections, handles)
• Data structures and their members

// Example inventory for "file I/O layer"
// Classes: FileReader, BufferedStream, PathResolver
// Functions: open(), read(), seek(), close()
// Types: std::ifstream, std::filesystem::path

3.2 How It Is Used

Document the patterns and conditions:

• Function signatures and parameter patterns
• Return value handling (error codes, exceptions, optionals)
• Conditional logic (when is X called vs Y?)
• Resource lifecycle (RAII patterns, manual management)
• Configuration and parameterization

// Example: "How is connection pooling used?"
// - Pool initialized with max_connections from config
// - get_connection() blocks if pool exhausted
// - Connections auto-returned via RAII wrapper
// - Timeout triggers reconnect logic

3.3 Where To Use It

Map call sites and triggering contexts:

• Which functions/methods initiate the usage?
• What's the call hierarchy? (entry point → ... → actual usage)
• What conditions trigger each pattern?
• Lifecycle timing (initialization, request handling, shutdown)

// Example call hierarchy for "data fetching"
// main()
//   → Application::run()
//     → RequestHandler::process()
//       → DataService::fetch()      // <-- actual usage
//         → Repository::query()

CHECKPOINT 2: Present findings for each area

## Deep Dive: [Area Name]

### What Is Used
| Component | Type | Purpose |
|-----------|------|---------|
| DataReader | class | Reads records from source |
| Config::timeout | member | Connection timeout in ms |
| fetch() | method | Retrieves data with filters |

### How It Is Used
| Pattern | Signature/Example | Conditions |
|---------|-------------------|------------|
| Filtered fetch | fetch(Filter f) | When user specifies criteria |
| Batch read | fetchBatch(size_t n) | For bulk operations |
| Retry on error | 3 retries with backoff | On connection failure |

### Where To Use It
| Call Site | Context | Trigger |
|-----------|---------|---------|
| Processor::run() | Main loop | Each iteration |
| Importer::load() | Startup | Once on init |

**Should I continue to next area, go deeper here, or adjust scope?**

Wait for user response.

Phase 4: Synthesis

After all areas explored:

CHECKPOINT 3: Present draft document structure

## Proposed Document Structure

1. **What Is Used** (Complete inventory)
   - [components to include]

2. **How It Is Used** (Patterns and conditions)
   - [patterns to document]

3. **Where To Use It** (Call sites and contexts)
   - [call hierarchies to include]

4. **Extraction Recommendations**
   - [interface suggestions, dependencies to handle]

**Adjustments needed?** (add sections, remove sections, change focus)

Wait for user approval before generating.

Phase 5: Generate Document

Create the final markdown file with:

Required Sections

1. What Is Used Complete inventory of components for the explored usage type:

2. How It Is Used Patterns, signatures, and conditions:

3. Where To Use It Call sites and triggering contexts:

4. Extraction Recommendations

• Suggested interface for extracted library
• Dependencies to bundle or abstract
• Breaking changes to anticipate
• Specific answers to user's original question

Output File Location

Default: planning/exploration-<topic>.md

This integrates with the planning workflow - exploration documents feed into planning-feature or planning-refactor skills.

Subagent Usage

For large codebases, use subagents for parallel exploration:

• Spawn separate subagents for independent areas
• Each subagent reports back with What/How/Where for its area
• Main agent synthesizes findings

Example: "Explore database layer" might spawn:

• Subagent 1: Read operations
• Subagent 2: Write operations
• Subagent 3: Connection management

Main Agent
    │
    ├── Subagent: "Explore read operations"
    │   └── Returns: What/How/Where for reads
    │
    ├── Subagent: "Explore write operations"
    │   └── Returns: What/How/Where for writes
    │
    └── Subagent: "Explore connection management"
        └── Returns: What/How/Where for connections

Main Agent synthesizes into single document

Red Flags - STOP and Check

• No usage type specified - User MUST specify what to explore (e.g., "database reading", "logging layer")
• Exploring without scoping - Go back and ask questions first
• Long silence - If you've read more than 5 files without user update, pause and report
• Missing what/how/where - Every finding should answer at least one of the three questions
• Generating without checkpoint - Always present draft structure before final document

Common Mistakes

Rationalizations to Reject

Integration with Other Skills

The exploration document (planning/exploration-<topic>.md) serves as input to planning skills.