How to Understand Code You Didn't Write — AI Code Explanation Guide

You just joined a team, inherited a codebase, or opened a pull request in a language you barely know. The code works, but you have no idea why. Here is a systematic approach to understanding any code you did not write — using AI explanation to accelerate the process.

The Problem

Every developer faces this regularly:

• New job — your first week, you are staring at 200 files someone else wrote with no documentation
• Inherited project — the original developer left, the code works, nobody knows how
• Pull request review — a teammate submitted 400 lines of changes and you need to approve it
• Stack Overflow answer — the accepted answer has code that solves your problem, but you do not understand the approach
• Cross-language work — you are a JavaScript developer and your team just added a Python microservice
• Open source contribution — you want to contribute to a project but need to understand the existing code first

Asking a colleague to explain every function is not sustainable. Reading documentation that does not exist is not possible. AI code explanation fills the gap.

Step-by-Step: Understanding Unfamiliar Code

Step 1 — Find the Entry Point

Every codebase has a starting point. Find it first:

Framework / Type	Entry Point File	What to Look For
React app	src/App.js or src/index.js	Main component, routes, providers
Node.js API	server.js or index.js	Express routes, middleware, port
Python app	main.py or app.py	Flask/Django routes, startup logic
Script / automation	The file you run	Top-level function calls, imports
SQL database	Schema file or migrations	Table structures, relationships

Paste the entry point into Code Explainer. The explanation tells you what the application does at the highest level.

Step 2 — Follow the Main Flow

From the entry point, identify the core functions and paste each one separately:

1. Read the explanation of function A — it calls function B and function C
2. Paste function B — understand what it does
3. Paste function C — understand what it does
4. Now you understand the full flow: A calls B which fetches data, then C which transforms it

Work outward like peeling an onion. Entry point first, core logic second, utility functions last.

Step 3 — Handle the Confusing Parts

Some code patterns are harder to read than others:

• Regex patterns — paste the regex into Regex Tester to see what it matches
• Nested callbacks or promise chains — paste the full chain into the code explainer for a flow breakdown
• SQL with multiple JOINs — paste the query to understand what data it pulls and how tables connect
• Configuration files — paste config objects to understand what each setting controls

Real Scenario: JavaScript Dev Reading Python

You know JavaScript. Your team just inherited a Python data pipeline. Here is exactly what to do:

1. Find the main script (usually main.py or pipeline.py)
2. Paste it into Code Explainer — get the high-level flow
3. The explanation says it reads a CSV, filters rows, groups by region, and writes results
4. You do not need to learn Python list comprehensions or pandas syntax — you now know what the code does
5. For each helper function the main script calls, paste and read
6. In 30 minutes, you understand a Python codebase without learning Python

Understanding Stack Overflow Code

Stack Overflow answers often provide working code without explaining the approach. Before copying code into your project:

1. Paste the answer code into the explainer
2. Read what it actually does — not just that it "works"
3. Decide if the approach fits your use case or if you need a different solution
4. Understand the code before you own it

Tips for Better Results

• Paste one function at a time — not entire files. Focused code produces focused explanations.
• Keep variable names and comments — they give the AI context about intent
• Use Code Formatter first — if the code is poorly formatted, clean it up before explaining. Readable code produces better explanations.
• Compare versions with Diff Checker — when reviewing changes, see what changed alongside what it does

When AI Explanation Is Not Enough

AI code explanation handles individual functions and code blocks well. It has limits:

• System architecture — how 50 files connect requires reading multiple files and building a mental map
• Business logic — why the code applies a 15% discount on Tuesdays requires domain knowledge, not code reading
• Performance implications — the explanation tells you what the code does, not whether it does it efficiently

For these cases, combine AI explanation with team conversations, existing documentation, and your own analysis.