Explain Code

Provide a layered explanation that starts simple and goes deeper on request.

Steps

1. Identify the target:
   • Read the file, function, class, or concept the user wants explained
   • If the target is vague (“explain the auth system”), identify the entry point and core files
2. Layer 1 — One-liner:
   • Explain what it does in a single sentence
   • Focus on the what, not the how
   • Example: “This function validates JWT tokens and attaches the decoded user to the request.”
3. Layer 2 — How it works (5-10 lines):
   • Walk through the high-level flow
   • Name the key steps without implementation details
   • Mention inputs, outputs, and side effects
   • Example: “It extracts the token from the Authorization header, verifies the signature using the secret from env, checks expiration, looks up the user in the database, and attaches them to req.user.”
4. Layer 3 — Implementation details (on request):
   • Walk through the code line by line or block by block
   • Explain why specific approaches were chosen
   • Point out error handling, edge cases, and guard clauses
   • Reference related files, types, or functions
5. Layer 4 — Context and connections (on request):
   • How this code fits into the larger system
   • What depends on it (callers, consumers)
   • What it depends on (services, libraries, config)
   • Historical context if visible from git blame or comments
6. Adapt to the reader:
   • If the user seems experienced: skip basics, focus on non-obvious behavior
   • If the user seems new: use analogies, avoid jargon, explain prerequisites
   • If unclear: default to Layer 2 and offer to go deeper

Output Format

**What it does:** [one-liner]

**How it works:**
1. [step]
2. [step]
3. [step]

**Key details:**
- [non-obvious behavior or edge case]
- [important dependency or assumption]

Want me to go deeper on any part?

Important

• Start simple, go deep on request. Don’t dump implementation details when the user just wants to understand the purpose.
• Use the user’s language. If they say “the login thing,” use that phrase — don’t correct them with “the OAuth2 authentication middleware.”
• Point out the non-obvious. The obvious parts are already in the code. Explain the why, the edge cases, and the gotchas.
• Be honest about uncertainty. If the code is unclear or you’re guessing at intent, say so.