Code explainer

Explain code, concepts, or system behavior with adjustable depth levels.

Purpose

Get clear explanations of:

How specific code works
Why certain patterns are used
What a system/module does
Architectural decisions and trade-offs

Instructions

Step 1: Determine scope

Identify what needs explanation:

File: Entire file structure and purpose
Function/Method: Specific implementation details
Concept: Architectural pattern or design decision
Flow: How data/control moves through the system

Step 2: Assess complexity

Simple (1-2 min read)     → Quick summary, key points only
Standard (3-5 min read)   → Purpose, how it works, key decisions
Deep (10+ min read)       → Full breakdown, alternatives, trade-offs

Step 3: Gather context

# For file explanations
head -50 "$FILE"  # See imports and structure

# For function explanations
grep -A 30 "function $NAME\|def $NAME\|fn $NAME" "$FILE"

# For module explanations
ls -la "$DIR"
cat "$DIR/index.ts" 2>/dev/null || cat "$DIR/__init__.py" 2>/dev/null

Step 4: Structure the explanation

Output format

📖 Explanation: [Target]

Scope: [file/function/concept/flow] Depth: [simple/standard/deep]

What it does

[1-3 sentences describing the purpose]

How it works

[Step-by-step breakdown appropriate to depth level]

Key decisions

Decision	Why	Alternative
[choice made]	[reasoning]	[what else could work]

Example usage

// How to use this correctly

Related code

path/to/related.ts - [relationship]
path/to/dependency.ts - [relationship]

💡 Learning Notes (if --learn flag)

[Additional context for understanding the broader pattern]

Depth levels

Simple (`/explain --simple`)

**validateUser()** checks if the user object has required fields
(email, password) and returns a boolean. Uses regex for email format.

Standard (`/explain` - default)

**validateUser(user: User): ValidationResult**

**Purpose**: Validates user input before database operations.

**Flow**:
1. Check required fields exist (email, password)
2. Validate email format with regex
3. Check password meets requirements (8+ chars, special char)
4. Return { valid: boolean, errors: string[] }

**Used by**: signup(), updateProfile()

Deep (`/explain --deep`)

[All of standard, plus:]

**Design Decisions**:
- Returns ValidationResult instead of throwing to allow batch validation
- Regex chosen over library for zero dependencies
- Password rules configurable via config.ts

**Trade-offs**:
- Pro: Fast, no dependencies
- Con: Regex email validation isn't RFC-compliant

**Alternatives Considered**:
- Zod schema: More powerful but adds 50KB
- Class-validator: Better for decorators but OOP-heavy

Usage examples

Explain a file:

/explain src/auth/middleware.ts

Explain a function:

/explain the handleWebhook function in payments.ts

Explain a concept:

/explain how our event sourcing works

Explain with specific depth:

/explain --deep the authentication flow
/explain --simple what useCallback does

Explain for learning:

/explain --learn the repository pattern used here

Tips

Be specific: "Explain line 45-60" > "Explain this file"
State your level: "I'm new to TypeScript" helps calibrate
Ask follow-ups: "Why not use X instead?" deepens understanding
Request analogies: "Explain like I'm familiar with Python but not TS"

$ARGUMENTS

explain