Reading other people's code
A systematic approach to understanding any codebase
⏱ Est. ~8 min
01 · Read
A secret that surprises most beginners: professional engineers spend more time reading code than writing it.
You join a team, switch projects, even come back to your own code weeks later — you need to understand code you didn't write (or don't remember writing). Randomly scrolling and hoping to figure it out doesn't work. You need a system.
The good news? Reading code is a skill, and like any skill it gets easier the more you practice. Let's learn a repeatable process that works on any codebase.
💡 Picture thisReading a new codebase is like exploring a new city. You don't start by wandering random streets. You look at the map first (README), see what's nearby (dependencies), find the main roads (entry points), and then explore the neighborhoods one by one (modules).
02 · Read
You just got handed someone else's project — a Task API. You've never seen this code. Let's apply the code-reading protocol step by step in the terminal.
03 · Terminal exercise
Code-reading protocol step 1: read the README. The README tells you what the project does, how to install it, and how to run it. Always look here first.
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04 · Terminal exercise
Step 2: look at package.json. Dependencies tell you what technology is used. Scripts tell you how to run and test it.
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05 · Terminal exercise
Step 3: find the entry point and scan the structure. You know from package.json that app.js is the entry point. Look at the folder structure first, then read the main file.
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06 · Step-through
The code-reading protocol — follow these steps for any new codebase
1. Read the README
README.md tells you what the project does, how to install it, and how to run it. Always look here first. No README also tells you something — the project might be poorly documented.
2. Look at package.json
Dependencies tell you what technology is used. Scripts tell you how to run and test it. Check "dependencies" for the main libraries and "scripts" for commands like "start", "test", and "build".
3. Scan the folder structure
How is the code organized? Look for src/, public/, routes/, models/ — these hint at the architecture. Everything in one flat folder means a small project. Nested folders with clear names mean it's well organized.
4. Find the entry point
Usually index.js, app.js, or main.js — that's where the program starts. The "main" field or "start" script in package.json will point you to it.
5. Follow the imports
From the entry point, follow require() or import statements to understand the dependency tree. Every import takes you to the next puzzle piece. Don't try to understand everything at once — map the connections first.
6. Ask Claude for help
With Claude Code: "give me an overview of this project" gets you a high-level summary instantly. Claude can read every file and give you a map of the codebase in seconds — what might take you hours by hand.
07 · Fill in the blank
When exploring a new project, the first file you read is the _____.
08 · Quiz
When exploring a new codebase, what should you read first?
- The biggest file in the project
- The README.md file
- Every JavaScript file from top to bottom
- The test files
Other lessons in this chapter
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