Codebase Overview

Core responsibilities:

• Discover project structure and tech stack
• Identify key modules and their responsibilities
• Document entry points and data flows
• Catalog patterns and conventions
• Use research skill for unclear modules

Flow: Discover → Classify → Document

• ./.gtd/CODEBASE.md

Agents used:

• research — For deep dives on unclear modules

Map, Don't Judge

Document what IS, not what SHOULD BE. Save opinions for later.

Breadth First, Depth on Demand

Start with directory structure. Go deep only when:

• Module is central to most features
• Purpose is unclear from naming
• Multiple entry points converge here

Living Document

CODEBASE.md is updated when:

• Major refactoring happens
• New domains are added
• Someone runs --refresh

No Guessing From Names

NEVER describe a module based on its name alone.

• UserService might delete users, not serve them
• utils/ might contain critical business logic
• cache.ts might write to database

Every description requires reading actual code.

Evidence Required

Every claim must cite evidence:

• Tech stack → cite package.json, go.mod, or actual imports
• Module purpose → cite key function signatures read
• Patterns → cite 2+ files demonstrating the pattern

No citation = don't write it.

Admit Unknowns

If you can't verify something, add it to Open Questions.

Better: "Open Question: What does core/ do?" Worse: "core/ contains core business logic" (guessed from name)

1. Check Mode

Check if $ARGUMENTS contains --refresh:

If REFRESH mode:

• Load existing ./.gtd/CODEBASE.md
• Compare against current codebase
• Update changed sections only

If NEW mode:

• Proceed to Discovery Phase

2. Discovery Phase

2.1 Project Root Scan

ls -la
cat package.json 2>/dev/null || cat Cargo.toml 2>/dev/null || cat go.mod 2>/dev/null || cat requirements.txt 2>/dev/null || echo "No manifest found"

Identify:

• Language/runtime
• Package manager
• Build system
• Key dependencies

2.2 Directory Structure

find . -type d -maxdepth 3 | grep -v node_modules | grep -v .git | grep -v __pycache__ | head -50

Map top-level directories:

• src/, lib/, app/ → Core code
• test/, tests/, __tests__/ → Test suites
• config/, .env* → Configuration
• scripts/, bin/ → Tooling
• docs/ → Documentation

2.3 Entry Points

Find entry points by convention:

• main.*, index.*, app.*
• server.*, cli.*
• package.json scripts
• Dockerfile CMD/ENTRYPOINT

2.4 Spawn Archaeologist Agent

Trigger: After mapping directory structure (Step 2.2). Concurrency: As many as needed.

Fill prompt and spawn:

<objective>
Analyze and classify modules in: {root_dir}
</objective>

<discovery_checklist>

1. Map Project Structure (directories, key files)
2. Classify Modules (Domain, Infra, API, Shared)
3. Identify Entry Points (HTTP, CLI, Workers)
4. Catalog Patterns (Naming, Error Handling, Testing)
   </discovery_checklist>

<output_format>
Codebase Map (CODEBASE.md draft):

- Tech Stack Summary
- Module Classification Table
- Entry Points List
- Observed Patterns
- Open Questions (for anything unclear)
  </output_format>

Task(
  prompt=filled_prompt,
  subagent_type="researcher",
  description="Mapping codebase architecture"
)

Note: The subagent will read files without polluting your main context.

2.5 Review Findings

Review the subagent's draft. If "Open Questions" remain, manually check or spawn another task.

3. Write CODEBASE.md

Bash:

mkdir -p ./.gtd

Write to ./.gtd/CODEBASE.md:

# Codebase Overview

**Generated:** {date}
**Last Updated:** {date}

## Tech Stack

| Layer     | Technology  |
| --------- | ----------- |
| Language  | {language}  |
| Runtime   | {runtime}   |
| Framework | {framework} |
| Database  | {database}  |
| ...       | ...         |

## Project Structure

{tree structure with annotations}

## Modules

### {Module Name}

**Path:** `{path}`
**Type:** {Domain | Infrastructure | API | Shared}
**Purpose:** {one-line description}

Key files:
- `{file}` — {responsibility}

### {Next Module}
...

## Entry Points

| Entry Point | Type | File | Purpose |
|-------------|------|------|---------|
| {name} | HTTP/CLI/Worker | {file} | {purpose} |

## Patterns & Conventions

(Only include patterns you verified in 2+ files. Cite examples.)

- **File naming:** {pattern}
- **Error handling:** {pattern}
- **Testing:** {pattern}

## Dependencies (Key)

| Dependency | Purpose |
|------------|---------|
| {name} | {why it's used} |

## Open Questions

- {Anything unclear that needs investigation}

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
 GTD ► CODEBASE OVERVIEW COMPLETE ✓
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Overview written to ./.gtd/CODEBASE.md

| Section | Items |
|---------|-------|
| Modules | {N} |
| Entry Points | {N} |
| Key Dependencies | {N} |

─────────────────────────────────────────────────────

▶ Next Up

/spec — define what you want to build (now with codebase context)

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