---

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

Ask for these if not provided:

• The code — the snippet or file to explain (paste it, or point at the path)
• The language or runtime — if it is not obvious from the code
• The reader — who this is for and how much they already know
• What they are trying to understand — the bug, the review, the handover; 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