I Built a Web Browser from Scratch in 42 Days

42 days ago I made a decision.

• Parse URLs into protocol, host, port, path


• Open raw TCP and TLS connections


• Build and send HTTP GET requests


• Parse HTTP responses including chunked encoding


• Tokenize raw HTML character by character


• Build a DOM tree using a stack


• Match CSS rules to DOM nodes


• Calculate layout (x, y, width, height) for every element


• Paint rectangles and text on a Canvas using Electron


• Execute JavaScript via eval()


• Navigate with back, forward, reload


• Multiple tabs with independent history


• Render real websites — today it rendered Wikipedia

What I learned

Before this project I knew how to use the web. Now I understand it.

TCP handshakes aren't magic. HTTP is just text. HTML is just tokens. CSS is just rules. A browser is just a pipeline.

Every abstraction that used to feel like magic now makes complete sense.

The most surprising thing — a layout engine is just two passes over a tree. Width flows down from parent to child. Height bubbles up from child to parent. That's it. That's what every browser does.

The hard days

Day 9 — built a DOM tree using a stack. Failed 6 times before it clicked.

Day 21 — layout engine born. Took 3 days to get width and height right.

Day 42 — fixed a bug where CSS inside style tags was breaking the entire DOM tree because my tokenizer treated > in CSS selectors as HTML tag endings.

Every bug taught me something real.

The code

github.com/Nitin-kumar-yadav1307/Courage

42 days. No libraries. Every line by hand.

This is just the beginning.