Codebase Archaeology

Core Insight: Don't read randomly. Documentation first, then follow data flow from entry points outward.

The Problem

You land in an unfamiliar codebase. Where do you start? Random file reading wastes context. You need a systematic approach that builds understanding efficiently and produces a reusable "mental model" of the architecture.

---

THE EXACT PROMPT

For Deep Investigation (Spawning Explore Agent)

Thoroughly explore this codebase. I need to understand:

1. Overall architecture and module structure
2. How data flows through the system (input → processing → output)
3. Key data structures (the 3-5 types everything revolves around)
4. The integration points (external APIs, databases, file I/O)
5. Configuration system (env vars, config files, CLI flags)
6. Test infrastructure

Focus on src/ directory structure and main modules. Map out how the pieces fit together.
Be very thorough - I need a complete mental model of how this codebase works.

For Self-Directed Exploration

I want you to sort of randomly explore the code files in this project, choosing
code files to deeply investigate and trace their functionality through related
files. Build a comprehensive mental model of the architecture.

---

Documentation First (Critical!)

Before touching code, ALWAYS read:

cat AGENTS.md     # Project-specific rules and architecture notes
cat README.md     # Purpose, installation, usage

Why this matters:

• AGENTS.md often contains architecture diagrams, key decisions, gotchas
• README.md reveals the project's purpose and main workflows
• Skipping this wastes time rediscovering documented knowledge

---

Quick Start

# Phase 1: Orientation (2 min)
cat AGENTS.md README.md | head -200    # DOCUMENTATION FIRST!
ls -la src/ lib/ cmd/ pkg/             # Directory structure
cat Cargo.toml package.json pyproject.toml  # Dependencies

# Phase 2: Entry Points (5 min)
rg "fn main|async fn main" --type rust   # Rust entry
rg "clap|structopt|argparse|commander" . # CLI frameworks
rg "Router|routes|@app\." .              # HTTP routers

# Phase 3: Core Types (5 min)
rg "^(pub )?struct |^class |^interface " --type rust --type ts --type py
rg "impl .* for" --type rust             # Trait implementations

# Phase 4: Data Flow (10 min)
# Trace from entry → handler → service → storage

---

The Layers

┌─────────────────────────────────────┐
│ ENTRY POINTS (start here)           │
│ main(), CLI commands, HTTP routes   │
└─────────────┬───────────────────────┘
              │
              ▼
┌─────────────────────────────────────┐
│ HANDLERS / CONTROLLERS              │
│ Request parsing, orchestration      │
└─────────────┬───────────────────────┘
              │
              ▼
┌─────────────────────────────────────┐
│ CORE DOMAIN                         │
│ Business logic, key types           │
└─────────────┬───────────────────────┘
              │
              ▼
┌─────────────────────────────────────┐
│ STORAGE / INTEGRATION               │
│ Database, files, external APIs      │
└─────────────────────────────────────┘

---

Agent-Assisted Exploration

For large codebases, spawn an Explore agent:

Task tool → subagent_type: "Explore"
Prompt: "Analyze the [project] codebase to provide a deep technical understanding.
Focus on:
1. Architecture Overview — how components interact
2. Key Data Structures — core types and their relationships
3. Data Flow — trace from ingestion to storage to output
4. Integration Points — external dependencies, APIs, databases"

Why agents help:

• They can read many files without filling your context
• They return a synthesized summary, not raw data
• You get architecture insights without the noise

---

Language-Specific Entry Points

Language	Entry Point	CLI Framework	HTTP Router
Rust	fn main() in main.rs	clap, structopt	axum, actix
TypeScript	index.ts, main.ts	commander, yargs	express, fastify
Python	__main__.py, main.py	argparse, click, typer	flask, fastapi
Go	main.go in cmd/	cobra, flag	chi, gin, echo

---

Critical Searches

# Find entry points
rg "fn main|def main|function main|export default" .

# Find configuration
rg "env\.|process\.env|os\.environ|std::env" .
rg "config|settings|options" --type-add 'cfg:*.{toml,yaml,json}' -t cfg

# Find key types (the 3-5 everything revolves around)
rg "^(pub )?(struct|class|interface|type) \w+" --type rust --type ts --type py

# Find external integrations
rg "fetch\(|reqwest|aiohttp|requests\." .          # HTTP clients
rg "query|execute|SELECT|INSERT" .                  # Database
rg "open\(|File::|fs\." .                           # File I/O

# Find error handling (reveals edge cases)
rg "Error|Exception|panic|unwrap|expect" .

---

Output Template

After exploration, produce a Comprehensive Technical Summary:

## [Project Name] - Technical Architecture Summary

### Executive Summary
**[Project]** is a [type] that [purpose]. It implements [key patterns].

**Key Statistics:**
- ~X lines of code across Y modules
- Language: [lang] [version]
- Key dependencies: [list]

---

### Entry Points
- `src/main.rs:15` — CLI entry, parses args via clap
- `src/routes/mod.rs:1` — HTTP router (axum)

### Key Types
| Type | Location | Purpose |
|------|----------|---------|
| `Project` | src/model.rs:10 | Core domain object |
| `Config` | src/config.rs:5 | Runtime configuration |
| `Storage` | src/storage.rs:1 | Persistence layer |

### Data Flow

CLI args → Config::load() → Project::process() → Storage::save()

### External Dependencies
- SQLite via rusqlite (persistence)
- reqwest (HTTP client)
- tokio (async runtime)

### Configuration
| Source | Example |
|--------|---------|
| Env var | `CONFIG_PATH=/etc/tool.toml` |
| Config file | `~/.config/tool/config.toml` |
| CLI flag | `--verbose` |

---

Anti-Patterns

Don't	Do
Skip AGENTS.md/README	Documentation first, always
Read files randomly	Follow entry point → data flow
Read entire files	Skim structure, dive into key functions
Ignore tests	Tests reveal intended behavior
Get lost in details	Build high-level map first
Fill context with raw code	Use Explore agent for synthesis

---

When to Use What

Situation	Approach
Brand new codebase	Full archaeology (all phases)
Adding a feature	Trace similar existing feature
Fixing a bug	Trace from symptom to root
Understanding one module	Start from module's public API
Large codebase (>10K LOC)	Spawn Explore agent first

---

Checklist

• Read AGENTS.md/README.md — Documentation first!
• Orientation: Directory structure, dependencies
• Entry points: main(), CLI commands, HTTP routes
• Key types: The 3-5 structs/classes everything uses
• Data flow: Entry → processing → storage
• Config: Env vars, config files, defaults
• Integration: External APIs, databases, file I/O
• Tests: What do tests reveal about intended behavior?
• Produce summary: Create reusable architecture doc

---

References

Need	File
Language-specific patterns	LANGUAGES.md
Common architecture patterns	PATTERNS.md
Example exploration sessions	EXAMPLES.md