---

name: code-explainer
description: "Explain what a piece of code does in plain English, at the depth the reader needs. Use when asked to explain code, walk through a function, understand an unfamiliar snippet, or onboard to a file. Produces a one-line summary, a step-by-step walkthrough, the non-obvious parts called out, and any bugs or smells spotted along the way."

Code Explainer Skill

Make unfamiliar code understandable — fast — without dumbing it down.

Working from a brief

Infer the language and intent from the code itself; label assumptions (assumed — confirm). Always produce a complete explanation even from a fragment. Match depth to the apparent level of the question.

Input

The code snippet or file, plus (if given) the language, the reader's level, and what they're trying to understand. Infer the rest.

Output Structure

In one line

What this code does, in a single sentence a busy reader can repeat.

Step by step

A walkthrough of the logic in order — group by block/function. Explain why, not just what, for anything non-trivial. Reference line ranges where helpful.

Worth knowing

The non-obvious bits: clever tricks, gotchas, side effects, complexity, dependencies, or assumptions the code makes.

Anything off?

Bugs, edge cases, or smells you noticed while reading — with the fix. (If it's clean, say so.)

Quality Checks

• The one-line summary stands alone
• The walkthrough explains why, not just restating the code in words
• Non-obvious behaviour (side effects, complexity, edge cases) is surfaced
• Any bug/smell spotted is flagged with a fix

Anti-Patterns

• Do not narrate line-by-line in English ("this line sets x to 5") — explain intent and structure
• Do not skip the gotchas — the value is in the non-obvious parts
• Do not assume expert level if the question reads like a beginner's (or vice-versa)
• Do not ignore a bug you can see just because you weren't asked to review it