Codebase Recon

Build context fast using scripts. Read files only after scripts tell you WHERE to look.

Core Principle

Scripts extract structure. LLMs interpret meaning.

Wrong approach: Read files → Hope to find what you need → Miss things → Waste tokens Right approach: Run targeted scripts → Get structured data → Read only relevant files → Complete picture

When to Use This Skill

Trigger recon when:

Starting work on an unfamiliar codebase
Planning a feature that touches multiple areas
Debugging and need to trace data flow
Asked "how does X work" or "where is Y used"
Need to understand dependencies or impact of changes

The Toolbelt

Scripts organized by what you're trying to learn. Run the script, interpret the output, THEN decide what files to read.

1. PROJECT DISCOVERY — What kind of project is this?

Detect project type and structure:

# Show project root structure (2 levels, ignore noise)
find . -maxdepth 2 -type f -name "*.json" -o -name "*.toml" -o -name "*.yaml" -o -name "*.yml" -o -name "Makefile" -o -name "Dockerfile" -o -name "*.mod" -o -name "*.lock" 2>/dev/null | head -30

# Quick file type census
find . -type f -name "*.ts" -o -name "*.tsx" -o -name "*.js" -o -name "*.jsx" -o -name "*.py" -o -name "*.go" -o -name "*.rs" -o -name "*.java" 2>/dev/null | sed 's/.*\.//' | sort | uniq -c | sort -rn

# Size of codebase (line count by extension)
find . -type f \( -name "*.ts" -o -name "*.tsx" -o -name "*.py" -o -name "*.go" \) -not -path "*/node_modules/*" -not -path "*/.git/*" 2>/dev/null | xargs wc -l 2>/dev/null | tail -1

Interpret: This tells you the tech stack, project structure, and scale before reading any code.

2. ENTRY POINTS — Where does execution start?

Find main entry points:

# Package.json scripts (JS/TS)
cat package.json 2>/dev/null | grep -A 20 '"scripts"'

# Main files
find . -maxdepth 3 -type f \( -name "main.*" -o -name "index.*" -o -name "app.*" -o -name "server.*" \) -not -path "*/node_modules/*" 2>/dev/null

# Python entry points
find . -maxdepth 3 -type f -name "__main__.py" -o -name "main.py" -o -name "app.py" -o -name "wsgi.py" 2>/dev/null

# Go entry points
grep -rl "func main()" --include="*.go" . 2>/dev/null | head -10

Interpret: These are the files to read FIRST — they show the application's skeleton.

3. DEPENDENCY MAP — What depends on what?

External dependencies:

# JS/TS - direct dependencies
cat package.json 2>/dev/null | grep -A 100 '"dependencies"' | grep -B 100 '"devDependencies"' | head -50

# Python - requirements
cat requirements.txt 2>/dev/null || cat pyproject.toml 2>/dev/null | grep -A 50 '\[project.dependencies\]'

# Go modules
cat go.mod 2>/dev/null | grep -v "^//"

Internal import graph (who imports whom):

# JS/TS - find all imports of a specific module
grep -rn "from ['\"].*modulename" --include="*.ts" --include="*.tsx" . 2>/dev/null

# Find the most-imported internal modules (hot files)
grep -roh "from ['\"]\..*['\"]" --include="*.ts" --include="*.tsx" . 2>/dev/null | sort | uniq -c | sort -rn | head -20

# Python imports
grep -rn "^from \|^import " --include="*.py" . 2>/dev/null | grep -v "__pycache__" | head -30

Interpret: Most-imported files are the core abstractions. Read those before anything else.

4. SYMBOL SEARCH — Where is X defined? Where is X used?

Find definition of a function/class/type:

# Find function definitions (JS/TS)
grep -rn "function FUNCNAME\|const FUNCNAME\|export.*FUNCNAME\|class FUNCNAME" --include="*.ts" --include="*.tsx" . 2>/dev/null

# Find function definitions (Python)
grep -rn "def FUNCNAME\|class FUNCNAME" --include="*.py" . 2>/dev/null

# Find all usages of a symbol
grep -rn "SYMBOLNAME" --include="*.ts" --include="*.tsx" --include="*.py" . 2>/dev/null | grep -v "node_modules"

Find type/interface definitions (TypeScript):

grep -rn "^export type\|^export interface\|^type \|^interface " --include="*.ts" --include="*.tsx" . 2>/dev/null | grep -v node_modules | head -30

Interpret: Now you know exactly which file(s) to read for a specific symbol.

5. API SURFACE — What endpoints/routes exist?

REST endpoints:

# Express.js routes
grep -rn "app\.\(get\|post\|put\|delete\|patch\)\|router\.\(get\|post\|put\|delete\|patch\)" --include="*.ts" --include="*.js" . 2>/dev/null | grep -v node_modules

# FastAPI/Flask routes (Python)
grep -rn "@app\.\(get\|post\|put\|delete\|route\)\|@router\." --include="*.py" . 2>/dev/null

# Next.js API routes (file-based)
find . -path "*/api/*" -name "*.ts" -o -path "*/api/*" -name "*.js" 2>/dev/null | grep -v node_modules

GraphQL:

# Find schema definitions
find . -name "*.graphql" -o -name "*.gql" 2>/dev/null | head -10

# Find resolvers
grep -rn "Query:\|Mutation:\|Resolver" --include="*.ts" --include="*.js" . 2>/dev/null | grep -v node_modules | head -20

Interpret: This maps the external interface before you read implementation details.

6. DATA LAYER — How is data stored/accessed?

Database schemas:

# Find migration files
find . -type d -name "migrations" -o -name "migrate" 2>/dev/null
find . -name "*.sql" -not -path "*/node_modules/*" 2>/dev/null | head -10

# Prisma schema
find . -name "schema.prisma" 2>/dev/null

# SQLAlchemy models
grep -rln "class.*Base\|Column(\|relationship(" --include="*.py" . 2>/dev/null | head -10

# TypeORM/Sequelize models
grep -rln "@Entity\|@Column\|Model.init" --include="*.ts" . 2>/dev/null | head -10

Interpret: Schema files define the data model — critical context for any data-touching feature.

7. CHANGE HISTORY — What's been touched recently?

Hot files (most frequently changed):

git log --pretty=format: --name-only --since="3 months ago" 2>/dev/null | sort | uniq -c | sort -rn | head -20

Recent changes to a specific area:

git log --oneline --since="1 month ago" -- "path/to/directory" 2>/dev/null | head -20

Who knows this code best:

git shortlog -sn -- "path/to/file" 2>/dev/null | head -5

Interpret: Hot files often contain bugs or are under active development. Recent changes show current focus areas.

8. ERROR PATTERNS — Where are errors handled?

Find error handling:

# Try/catch blocks
grep -rn "try {" --include="*.ts" --include="*.tsx" . 2>/dev/null | grep -v node_modules | wc -l

# Custom error classes
grep -rn "extends Error\|class.*Error" --include="*.ts" --include="*.py" . 2>/dev/null | grep -v node_modules

# Error boundaries (React)
grep -rln "componentDidCatch\|ErrorBoundary" --include="*.tsx" --include="*.jsx" . 2>/dev/null

Find logging:

grep -rn "console\.\(log\|error\|warn\)\|logger\.\|logging\." --include="*.ts" --include="*.py" . 2>/dev/null | grep -v node_modules | head -20

Interpret: Error handling patterns show how the codebase expects to fail — useful for debugging.

9. TEST COVERAGE — What's tested?

Find test files:

find . -name "*.test.ts" -o -name "*.spec.ts" -o -name "test_*.py" -o -name "*_test.py" -o -name "*_test.go" 2>/dev/null | grep -v node_modules | head -20

Test to source ratio:

# Count test files vs source files
echo "Test files:" && find . -name "*.test.*" -o -name "*.spec.*" -o -name "test_*" 2>/dev/null | grep -v node_modules | wc -l
echo "Source files:" && find . -name "*.ts" -o -name "*.py" 2>/dev/null | grep -v node_modules | grep -v test | grep -v spec | wc -l

Interpret: Test files show expected behavior and edge cases — often clearer than reading implementation.

10. CONFIG & ENVIRONMENT — How is it configured?

Find all config files:

find . -maxdepth 2 -name "*.config.*" -o -name ".env*" -o -name "*.toml" -o -name "*.yaml" -o -name "*.yml" 2>/dev/null | grep -v node_modules | head -20

Environment variables used:

grep -roh "process\.env\.[A-Z_]*\|os\.environ\[.*\]\|os\.getenv" --include="*.ts" --include="*.js" --include="*.py" . 2>/dev/null | sort | uniq

Interpret: Config files reveal deployment modes, feature flags, and integration points.

Recon Workflow

When you need codebase context, follow this sequence:

Project Discovery (30 seconds)
- Run project type detection
- Get file census
- Understand scale
Map the skeleton (1-2 minutes)
- Find entry points
- Map dependencies (most-imported files)
- Identify API surface
Targeted deep-dive (as needed)
- Symbol search for specific functions
- Read only the files scripts pointed you to
- Use git history to understand evolution
Build mental model
- Entry point → Core abstractions → Data layer → External interfaces
- Now you understand the codebase without reading every file

Script Selection Guide

I need to understand...	Run these scripts
What kind of project this is	Project Discovery
Where execution starts	Entry Points
The core abstractions	Dependency Map (most-imported)
Where a function is defined	Symbol Search (definition)
What uses a function	Symbol Search (usages)
The API surface	API Surface scripts
The data model	Data Layer scripts
What's actively being worked on	Change History (hot files)
How errors are handled	Error Patterns
Expected behavior	Test Coverage (read tests)

Anti-Patterns

Don't do this	Do this instead
Read files hoping to find what you need	Run symbol search, then read specific files
Start with implementation details	Start with entry points and work outward
Read all files in a directory	Find most-imported files, read those first
Guess at project structure	Run project discovery first
Ignore test files	Tests document expected behavior clearly
Read code without history	Check git log for context on why

Adapting Scripts

The scripts above are templates. Adapt them:

Replace file extensions for your stack
Adjust grep patterns for your framework
Add project-specific patterns (your error classes, your route patterns)
Combine with ripgrep (rg) if available — much faster

<constraint> Never read files blindly — run recon scripts first. Never start with implementation details — map the skeleton first. Never assume project structure — detect it. Always prefer targeted symbol search over full-file reading. Use git history to understand WHY code exists, not just WHAT it does. </constraint>

codebase-recon

SKILL.mdskills/codebase-recon/SKILL.md